Basic Java script handouts for students

Introduction

JavaScript is a object-based scripting language and it is light weighted. It is first implemented by

Netscape (with help from Sun Microsystems). JavaScript was created by Brendan Eich at

Netscape in 1995 for the purpose of allowing code in web-pages (performing logical operation on

client side).

It is not compiled but translated. JavaScript Translator is responsible to translate the JavaScript

code which is embedded in browser.

Netscape first introduced a JavaScript interpreter in Navigator 2. The interpreter was an extra

software component in the browser that was capable of interpreting JavaSript source code inside

an HTML document. This means that web page developer no need other software other than a

text editor of develop any web page.

Why we Use JavaScript?

Using HTML we can only design a web page but you can not run any logic on web browser like

addition of two numbers, check any condition, looping statements (for, while), decision making

statement (if-else) at client side. All these are not possible using HTML So for perform all these

task at client side you need to use JavaScript.

Where it is used?

It is used to create interactive websites. It is mainly used for:

Client-side validation

Dynamic drop-down menus

Displaying data and time

Build small but complete client side programs .

Displaying popup windows and dialog boxes (like alert dialog box, confirm

dialog box and prompt dialog box)

Displaying clocks etc.

History

JavaScript is a object-based scripting language and it is light weighted. It is first implemented

by Netscape (with help from Sun Microsystems). JavaScript was created by Brendan Eich at

Netscape in 1995 for the purpose of allowing code in web-pages (performing logical operation on

client side).

Using HTML we can only design a web page but you can not run any logic on web browser like

addition of two numbers, check any condition, looping statements(for, while), decision making

statement(if-else) etc. All these are not possible using HTML so for perform all these task we use

JavaScript.

Using HTML we can only design a web page if we want to run any programs like c programming

we use JavaScript. Suppose we want to print sum of two number then we use JavaScript for

coding.

Features of JavaScript

JavaScript is a client side technology, it is mainly used for gives client side validation, but it have

lot of features which are given below;

JavaScript is a object-based scripting language.

Giving the user more control over the browser.

It Handling dates and time.

It Detecting the user's browser and OS,

It is light weighted.

JavaScript is a scripting language and it is not java.

JavaScript is interpreter based scripting language.

JavaScript is case sensitive.

JavaScript is object based language as it provides predefined objects.

Every statement in javascript must be terminated with semicolon (;).

Most of the javascript control statements syntax is same as syntax of

control statements in C language.

An important part of JavaScript is the ability to create new functions

within scripts. Declare a function in JavaScript using function keyword.

Uses of JavaScript

There are too many web applications running on the web that are using JavaScript technology

like gmail, facebook,twitter, google map, youtube etc.

Uses of JavaScript

Client-side validation

Dynamic drop-down menus

Displaying data and time

Validate user input in an HTML form before sending the data to a server.

Build forms that respond to user input without accessing a server.

Change the appearance of HTML documents and dynamically write HTML

into separate Windows.

Open and close new windows or frames.

Manipulate HTML "layers" including hiding, moving, and allowing the

user to drag them around a browser window.

Build small but complete client side programs .

Displaying popup windows and dialog boxes (like alert dialog box, confirm

dialog box and prompt dialog box)

Displaying clocks etc.

Comment

Comment is nothing but it is a statement which is not display on browser window. it is useful to

understand the which code is written for what purpose.

Comments are useful in every programming language to deliver message. It is used to add

information about the code, warnings or suggestions so that the end user or other developer can

easily interpret the code.

Types of JavaScript Comments

There are two types of comments are in JavaScript

Single-line Comment

Multi-line Comment

Single-line Comment

It is represented by double forward slashes (//). It can be used before any statement.

Example

<script> // It is single line comment document.write("Hello Javascript"); </script>

Result

Hello Javascript

Multi-line Comment

It can be used to add single as well as multi line comments.

It is represented by forward slash (/) with asterisk (*) then asterisk with forward slash.Example

<script> /* It is multi line comment. It will not be displayed */ document.write("Javascript multiline comment");

</script>

JavaScript First Program

Javascript simple example to verify age of any person, if age is greater than 18 show message

adult otherwise show under 18

JavaScript Example to verify age

Example

<html><head><script>function verify(){var no;no=Number(document.getElementById("age").value);if(no<18){alert("Under 18");}else{alert("You are Adult");}}</script></head><body>Enter your age:<input id="age"><br /><button onclick="verify()">Click me</button></body></html>

Result

Enter your age:

Click me

Way of Using JavaScript

There are three places to put the JavaScript code.

Between the <body> </body> tag of html (Inline JavaScript)

Between the <head> </head> tag of html (Internal JavaScript)

In .js file (External JavaScript)

Inline JavaScript

When java script was written within the html element using attributes related to events of the

element then it is called as inline java script.

Example of Inline JavaScript

Example

<html><form><input type="button" value="Click" onclick="alert('Button Clicked')"/></form></html>

Result

Internal JavaScript

When java script was written within the section using element then it is called as internal java

script.

Example of Internal JavaScript

Example

<html><head> <script>function msg(){alert("Welcome in JavaScript");}</script></head><form><input type="button" value="Click" onclick="msg()"/></form></html>

Result

External JavaScript

Writing java script in a separate file with extension .js is called as external java script. For adding

the reference of an external java script file to your html page, use tag with src attribute as follows

Example

<script type="text/javascript" src="filename.js"/>

Create a file with name functions.js and write the following java script functions in it.

message.jsExample

function msg(){ alert("Hello Javatpoint"); }

Create a html page and use the file functions.js as follows

index.htmlExample

<html> <head> <script type="text/javascript" src="message.js"></script> </head> <body> <form> <input type="button" value="click" onclick="msg()"/> </form> </body> </html>

Result

Variable Declaration

Java script did not provide any data types for declaring variables and a variable in java script can

store any type of value. Hence java script is loosely typed language. We can use a variable

directly without declaring it.

Only var keyword are use before variable name to declare any variable.Syntax

var x;

Rules to declaring a variable

Name must start with a letter (a to z or A to Z), underscore( _ ), or

dollar( $ ) sign.

After first letter we can use digits (0 to 9), for example value1.

Javascript variables are case sensitive, for example x and X are different

variables.

Variable declaration

Example

var x = 10; // Validvar _value="porter"; // Validvar 123=20; // Invalidvar #a=220; // Invalidvar *b=220; // Invalid

Example of Variable declaration in JavaScript

Example

<script>var a=10;var b=20;var c=a+b;document.write(c);</script>

Output

30

Types of Variable in JavaScript

Local Variable

Global Variable

Local Variable

A variable which is declared inside block or function is called local variable. It is accessible within

the function or block only. For example:

Example

<script>

function abc(){ var x=10; //local variable } </script>

or

Example

<script> If(10<13){ var y=20;//javascript local variable } </script>

Global Variable

A global variable is accessible from any function. A variable i.e. declared outside the function or

declared with window object is known as global variable. For example:

Syntax

<script> var value=10;//global variable function a(){ alert(value); } function b(){ alert(value); } </script>

Declaring global variable through window object

The best way to declare global variable in javascript is through the window object. For example:

Syntax

window.value=20;

Now it can be declared inside any function and can be accessed from any function. For example:

Example

function m(){ window.value=200; //declaring global variable by window object } function n(){ alert(window.value); //accessing global variable from other function }

Example of JavaScript

Here i will show you how to write you first javascript code, you only need to write your javascript

code inside <script> ..... </script> tag using any editor like notepad or edit plus. Save below code

with .html or .htm extension. No need to compile your javascript code just open your code in any

web browser.

Find sum of two number using JavaScript

Example

<!doctype html><html><head>

<script>function add(){var a,b,c;a=Number(document.getElementById("first").value);b=Number(document.getElementById("second").value);c= a + b;document.getElementById("answer").value= c;}</script></head><body><input id="first"><input id="second"><button onclick="add()">Add</button><input id="answer"></body></html>

Result

Enter First Number:

Enter Second Number:

Add 

Code Explanation

no=Number(document.getElementById("first").value);This code is used for receive first input value form input field which have

id first.

no=Number(document.getElementById("second").value);This code is used for receive first input value form input field which have

id second.

document.getElementById("answer").value= fact;This code is used for receive calculated value of factorial and display in

input field which have id answer

<button onclick="add()">Add</button>This code is used for call add function when button clicked.

Find Factorial of number in JavaScript

Using javascript you can find factorial of any number, here same logic are applied like c language

you only need to write your javascript code inside <script> ..... </script> tag using any editor like

notepad or edit plus. Save below code with .html or .htm extension. No need to compile your

javascript code just open your code in any web browser.

Find factorial of number using JavaScript

Example Factorial of any number

<!doctype html><html><head><script>function show(){

var i, no, fact;fact=1;no=Number(document.getElementById("num").value);for(i=1; i<=no; i++) {fact= fact*i;} document.getElementById("answer").value= fact;}</script></head><body>Enter Num: <input id="num"><button onclick="show()">Factorial</button><input id="answer">

</body></html>

Result

Enter Num:   Factorial 

Code Explanation

no=Number(document.getElementById("num").value);This code is used for receive input value form input field which have id

num.

document.getElementById("answer").value= fact;This code is used for receive calculated value of factorial and display in

input field which have id answer

<button onclick="show()">Factorial</button>This code is used for call show function when button clicked.

If else Statement

The if statement is used in JavaScript to execute the code if condition is true or false. There are

three forms of if statement.

If Statement

If else statement

if else if statement

JavaScript If statement

if is most basic statement of Decision making statement. It tells to program to execute a certain

part of code only if particular condition or test is true.

Syntax

Syntax

if(expression){ //set of statements }

Example

<script> var a=10; if(a>5){ document.write("value of a is greater than 5"); } </script>

JavaScript if-else statement

In general it can be used to execute one block of statement among two blocks.

Syntax

if(expression){ //set of statements } else{//set of statements }

Example of if..else statement

<script> var a=40; if(a%2==0){

document.write("a is even number"); } else{ document.write("a is odd number"); } </script>

Result

a is even number

JavaScript If...else if statement

It evaluates the content only if expression is true from several expressions.

Syntax

if(expression1){ //content to be evaluated if expression1 is true } else if(expression2){ //content to be evaluated if expression2 is true } else{ //content to be evaluated if no expression is true }

Example of if..else if statement

<script> var a=40; if(a==20){document.write("a is equal to 20"); }

else if(a==5){document.write("a is equal to 5"); }else if(a==30){document.write("a is equal to 30"); } else{ document.write("a is not equal to 20, 5 or 30"); } </script>

Looping Statement in

Set of instructions given to the compiler to execute set of statements until condition becomes

false is called loops. The basic purpose of loop is code repetition.

The way of the repetition will be forms a circle that's why repetition statements are called loops.

Some loops are available In JavaScript which are given below.

while loop

for loop

do-while

while loop

When we are working with while loop always pre-checking process will be occurred. Pre-checking

process means before evolution of statement block condition part will be executed. While loop will

be repeats in clock wise direction.

Syntax

while (condition) {code block to be executed}

Example of while loop

<script> var i=10; while (i<=13) { document.write(i + "<br/>"); i++; } </script>

Result

10

11

12

13

do-while loop

In implementation when we need to repeat the statement block at least 1 then go for do-while. In

do-while loop post checking of the statement block condition part will be executed.

syntax

do{ code to be executed increment/decrement}while (condition);

Example of do-while loop

Example

<script> var i=11; do{ document.write(i + "<br/>"); i++; }while (i<=15); </script>

Result

11

12

13

14

15

for Loop

For loop is a simplest loop first we initialized the value then check condition and then increment

and decrements occurred.

Steps of for loop

Syntax

for (initialization; condition; increment/decrement){code block to be executed}

Example of for loop

Example

<script> for (i=1; i<=5; i++) { document.write(i + "<br/>") } </script>

Switch Statement

The switch statement is used in JavaScript to execute one code from multiple expressions.

Example

switch(expression){case value1:statement;break; case value2:statement;break; ......

default: statement;

}

Note: default code to be executed if above values are not matched

Note: in switch statement all the cases will be evaluated if we do not use break statement.

Example of switch statement in javascript.

Example

<script> var grade='B'; var result; switch(grade){ case 'A': result="A Grade"; break; case 'B': result="B Grade"; break; case 'C': result="C Grade"; break; default: result="No Grade"; } document.write(result); </script>

Result

Output: B Grade

Example of switch case in javascript

Example

<html><head>

<script>function myFunction() { var day; day=Number(document.getElementById("first").value); switch (day) { case 1: day = "Sunday"; break; case 2: day = "Monday"; break; case 3: day = "Tuesday"; break; case 4: day = "Wednesday"; break; case 5: day = "Thursday"; break; case 6: day = "Friday"; break; case 7: day = "Saturday"; break;default:day="Enter valid number" } document.getElementById("demo").innerHTML =day;}</script></head><body>

<p>Enter any number (1 to 7):</p><input id="first"><button onclick="myFunction()">Try it</button><p id="demo"></p></body></html>

Result

Enter any number (1 to 7):

 Try it

Function

An important part of JavaScript is the ability to create new functions within <script> and </script>

tag. Declare a function in JavaScript using function keyword. The keyword function precedes

the name of the function.Syntax

function functionName(parameter or not){..................}

Example of JavaScript using Function

Example

<html><head><script>function getname()

{name=prompt("Enter Your Name");alert("Welcome Mr/Mrs " + name);}</script></head><form><input type="button" value="Click" onclick="getname()"/></form></html>

Example

Array in JavaScript

Array are used to represents the group of elements into a single unit or consecutive memory

location. Each and every element what we are entering into the array is going to be stored in the

array with the unique index starting from zero. Through the indexes we can store the data or

elements into the array or we can get the elements from the array.

To declare an array in javascript we need new keyword. To create an array you use new Array(n)

where n was the number of slots in the array or new Array() omitting the size of an array.

Note: Whenever we create any array in javaScript without specifying the size then it well create

array object with the zero size.Syntax

myarray = new array(5);

Example of array in JavaScript

Example

<html><head>

<script type="text/javascript">function arrayex(){myarray = new Array(5)myarray[0] = 10myarray[1] = 20myarray[2] = 30myarray[3] = 40myarray[4] = 50sum = 0;

for (i=0; i<myarray.length; i++){sum = sum + myarray[i];}alert(sum)}</script></head><body><input type="button" onclick="arrayex()" value="click here"></body></html>

Result

Function used in Array

Here we will discuss about some functions which are frequently used in array concept in

JavaScript.

Function Discription

concat() To concats the elements of one array at the end of another array and returns an array.

sort() To sort all elements of an array.

reverse() To reverse elements of an array.

slice() To extract specified number of elements starting from specified index without deleting them from array.

splice() It will extract specified number of elements starting from specified index and deletes them from array.

push() To push all elements in array at top.

pop() To pop the top elements from array.

JavaScript Dialog box

All JavaScript dialog box is a predefined function which is used for to perform different-different

task. Some function are given below;

function Discription

alert() To give alert message to user.

prompt() To input value from used.

confirm() To get confirmation from user before executing some task.

Alert()

Alert function of java script is used to give an alert message to the user.

Alert function example

Example

<!doctype html><html><head><script>function alertmsg()

{alert("Alert function call");}</script></head><form><input type="button" value="Click Me" onclick="alertmsg()"/></form></html>

Result

prompt()

Prompt function of java script is used to get input from the user.

prompt() function example

Example

<!doctype html><html><head><script>function alertmsg(){a=prompt("Enter your name:");alert(a);}</script></head><form><input type="button" value="Click Me" onclick="alertmsg()"/></form></html>

Result

confirm()

confirm function of java script is used to get confirmation from user before executing some task.

confirm() function example

Example

<!doctype html><html><head><script>function alertmsg(){a=prompt("Enter your name:");confirm(a);}</script></head><form><input type="button" value="Click Me" onclick="alertmsg()"/></form></html>

Result

Window Object

The window object represents a window in browser. An object of window is created

automatically by the browser.

Window is the object of browser, it is not the object of javascript. The javascript objects are string,

array, date etc. It is used to display the popup dialog box such as alert dialog box, confirm dialog

box, input dialog box etc.

The window methods are mainly for opening and closing new windows. The following are the

main window methods. They are:

Methods of window object

Method Description

alert() displays the alert box containing message with ok button.

confirm() Displays the confirm dialog box containing message with ok and cancel button.

prompt() Displays a dialog box to get input from the user.

open() Opens the new window.

close() Closes the current window.

setTimeout() Performs action after specified time like calling function, evaluating expressions

etc.

Document Object

The document object represents the whole html document. When html document is loaded in

the browser, it becomes a document object. It is the root element that represents the html

document.

Methods of document object

Method Description

write("string") writes the given string on the document.

writeln("string") Same as write(), but adds a newline character after each statement.

getElementById() returns the element having the given id value.

getElementsByName() returns all the elements having the given name value.

getElementsByTagName() returns all the elements having the given tag name.

getElementsByClassName() returns all the elements having the given class name.

Event in JavaScript

All objects have properties and methods. In addition, some objects also have "events". Events

are things that happen, usually user actions, that are associated with an object. The "event

handler" is a command that is used to specify actions in response to an event. Below are some of

the most common events:

Event Discription

onLoad Occurs when a page loads in a browser

onUnload occurs just before the user exits a page

onMouseOver occurs when you point to an object

onMouseOut occurs when you point away from an object

onSubmit occurs when you submit a form

onClick occurs when an object is clicked

Events and Objects

Events are things that happen, actions, that are associated with an object. Below are some

common events and the object they are associaated with:

Event Object

onLoad Body

onUnload Body

onMouseOver Link, Button

onMouseOut Link, Button

onSubmit Form

onClick Button, Checkbox, Submit, Reset, Link

getElementById

The document.getElementById() method returns the element of specified id. In below example

we receive input from input field by using document.getElementById() method, here

document.getElementById() receive input value on the basis on input field id. In below example

"number" is the id of input field.Example

<html><body><head><script type="text/javascript"> function squre(){ var num=document.getElementById("number").value; alert(num*num); } </script> </head><form> Enter No:<input type="text" id="number" name="number"/><br/> <input type="button" value="squre" onclick="squre()"/> </form></body>

</html>

Result

Enter No:

Code Explanation

var num=document.getElementById("number").value; In this code getElementById received

value from input field which have id number.

Square of any number in javascript

Example

<html><body><head><script type="text/javascript"> function squre(){ var num=document.getElementById("number").value; var result=num*num; document.getElementById("answer").value=result;} </script> </head><form>Enter No:<input type="text" id="number" name="number"/><input type="button" value="squre" onclick="squre()"/><input id="answer"/></form></body></html>

Result

Enter No:   

JavaScript Forms Validation

Forms validation is important things other wise user input wrong data, so we need to validate

given data by user before submit it on server.

The JavaScript provides the facility to validate the form on the client side so processing will be

fast than server-side validation. So, most of the web developers prefer client side form validation

using JavaScript.

Here i will show you how to validate any input field like user name can not be blank. In below

example input are can not be blank.

Example

<html><head><script> function form_validation(){ var name=document.myform.name.value;

//var x = document.forms["myform"]["name"].value;

if (name==null || name==""){ alert("Name can't be blank"); return false; } }</script> </head>

<body> <form name="myform" method="post" action="register.php" onsubmit="return form_validation()" > Name: <input type="text" name="name"> <input type="submit" value="submit">

</form> </body></html>

Result

Name:   

Email validation

We can validate the email with the help of JavaScript. Here we check the condition related to any

email id, like email if must have "@" and "." sign and also email id must be at least 10 character.

There are many criteria that need to be follow to validate the email id such as:

email id must contain the @ and . character

There must be at least one character before and after the @.

There must be at least two characters after . (dot).Example

<html><head><script>function email_validation() { var x=document.myform.email.value; var atposition=x.indexOf("@"); var dotposition=x.lastIndexOf("."); if (atposition<1 || dotposition<atposition+2 || dotposition+2>=x.length){ alert("Please enter a valid e-mail address \n atpostion:"+atposition+"\n dotposition:"+dotposition); return false; } } </script>

submit

</script></head><body><form name="myform" method="post" action="#" onsubmit="return email_validation();"> Email: <input type="text" name="email"><br/> <input type="submit" value="register"> </form></body></html>

Result

Email: 

JavaScript Password Validation

Here i will show you how to validate any password field like password field can not be blank and

length of password is minimum 8 character.

Example

<html><head><script>function pass_validation(){ var password=document.myform.password.value;

if (password==null || password==""){ alert("password can't be blank"); return false; }else if(password.length<8){ alert("Password must be at least 8 characters long.");

register

return false; } }

</script></head><body><form name="myform" method="post" action="register.php" onsubmit="return pass_validation()" > Password: <input type="password" name="password"> <input type="submit" value="submit"> </form> </body></html>

Result

Password:   

Re-type Password Validation

Example

<html><head><script>function pass_validation(){var firstpassword=document.f1.password1.value; var secondpassword=document.f1.password2.value;

if(firstpassword==secondpassword){ return true; } else{ alert("password one and two must be same!");

submit

return false; } } </script></head>

<body><form name="f1" action="/JavaScript/Index" onsubmit="return pass_validation()"> Password:<input type="password" name="password1" /><br/> Re-enter Password:<input type="password" name="password2"/><br/> <input type="submit"> </form> </body></html>

Result

Password:

Re-enter Password:

JavaScript Interview Questions

What is JavaScript ?

JavaScript is a scripting language. It is object-based scripting language. It is light weighted. It is

different from Java language. It is widely used for client side validation.

JavaScript is which type of Language ?

JavaScript is a object-based scripting language. It is light weighted.

Why we use JavaScript ?

Using Html we can only design a web page. Using Html we can not run any logic on web browser

like addition of two numbers, check any condition, looping statements(for, while), decision making

Submit

statement(if-else) etc at client side. All these are not possible using Html so for perform all these

task at client side we use JavaScript.

Where JavaScript is used ?

It is used to create interactive websites. It is mainly used for:

Client-side validation

Dynamic drop-down menus

Displaying data and time

Build small but complete client side programs .

Displaying popup windows and dialog boxes (like alert dialog box, confirm

dialog box and prompt dialog box)

Displaying clocks etc.

What is the difference between == and ===

The 3 equal signs (===) mean "equality without type coercion". Using the triple equals, the values

must be equal in type as well. It checks for equality as well as the type.

== means simple equal to, it compare two values only. It checks equality only,

Example

== is equal to === is exactly equal to (value and type)0==false // true 0===false // false, because they are of a different type1=="1" // true, auto type coercion1==="1" // false, because they are of a different type

How to declare variable in JavaScript ?

Java script did not provide any data types for declaring variables and a variable in java script can

store any type of value. We can use a variable directly without declaring it. Only var keyword are

use before variable name to declare any variable.

Syntax

var x;

Difference between Window object and document object

Document object Window object

The document object represents the whole html document. When html document is loaded in the browser, it becomes a document object.

The window object represents a window in browser. An object of window is created automatically by the browser.

What would be the difference if we declare two variables inside a JavaScript, one with 'var' keyword and another without 'var' keyword ?

The variable with var keyword inside a function is treated as Local variable, and the variable

without var keyword inside a function is treated a global variable.

What is a closure in JavaScript ?

JavaScript allows you to declare a function within another function, and the local variables still

can be accessible even after returning from the function you called.

In other words, a closure is the local variables for a function which is kept alive after the function

has returned.

What is uses of Window Object ?

The window object represents a window in browser. An object of window is created automatically

by the browser. It is used to display the popup dialog box such as alert dialog box, confirm dialog

box, input dialog box etc.

What is Document Object

The document object represents the whole html document. When html document is loaded in the

browser, it becomes a document object. It is the root element that represents the html document.

Is JavaScript case sensitive ?

Yes!

A function getElementById is not the same as getElementbyID

What does "1"+2+3 evaluate to ?

After a string all the + will be treated as string concatenation operator (not binary +), so the result

is 123.

What does 1+2+"5" evaluate to ?

If there is numeric value before and after +, it is treated is binary + (arithmetic operator), so the

result is 35.

Difference between get and post method.

Http protocol mostly use either get() or post() methods to transfer the request.

Get method Post method

1 Request sends the request parameter as query string appended at the end of the request.

Post request send the request parameters as part of the http request body.

2 Get method is visible to every one (It will be displayed in the address bar of browser ).

Post method variables are not displayed in the URL.

3 Restriction on form data, only ASCII characters allowed.

No Restriction on form data, Binary data is also allowed.

4 Get methods have maximum size is 2000 character.

Post methods have maximum size is 8 mb.

5 Restriction on form length, So URL length is restricted No restriction on form data.

6 Remain in browser history. Never remain the browser history.

How to create function in JavaScript ?

Declare a function in JavaScript using function keyword. The keyword function precedes the

name of the function.

Syntax

function function_name(){ //function body }

Read more.......

How to write comment in JavaScript ?

There are two types of comment are available in JavaScript.

Single Line Comment: It is represented by // (double forward slash)

Multi Line Comment: It is represented by slash with asterisk symbol as /*

write comment here */

How do we add JavaScript onto a web page?

There are several way for adding javascript on a web page but there are two way with is

commonly used by developers

Between the <body> </body> tag of html (Inline JavaScript)

Between the <head> </head> tag of html (Internal JavaScript)

In .js file (External JavaScript)

Read more .......

How to access the value of a textbox using JavaScript ?

Example

<!DOCTYPE html><html><body>Name: <input type="text" id="txtname" name="FirstName" value="Porter"></body></html>

There are following way to access the value of the above textbox

Example

var name = document.getElementById('txtname').value;alert(name);or we can use the old waydocument.forms[0].mybutton.var name = document.forms[0].FirstName.value;

alert(name);

Note: This uses the "name" attribute of the element to locate it.

How you will get the CheckBox status whether it is checked or not ?

Example

var status = document.getElementById('checkbox1').checked; alert(status); //it will return true or false

How to create arrays in JavaScript ?

Example

var names = new Array();

// Add Elements in Arraynames[0] = "Hina";names[1] = "Niki";names[2] = "Ram";

// This is second wayvar names = new Array("Hina", "Niki", "Ram");

If an array with name as "marks" contain three elements then how you will print the third element of this array?

Example

Print third array element document.write(marks[2]);

Note: Array index start with 0

What does the isNaN() function ?

The isNan() function returns true if the variable value is not a number.

Example

document.write(isNaN("Hello")+ "<br>");document.write(isNaN("2015/04/29")+ "<br>");document.write(isNaN(1234)+ "<br>");

Output

true

true

false

What is the use of Math Object in Javascript?

The math object provides you properties and methods for mathematical constants and functions.

Example

var x = Math.PI; // Returns PI

var y = Math.sqrt(25); // Returns the square root of 25

var z = Math.sin(60); Returns the sine of 60

How can you submit a form using JavaScript?

To submit a form using JavaScript use document.form[0].submit();

Does JavaScript support automatic type conversion?

Yes JavaScript does support automatic type conversion, it is the common way of type conversion

used by JavaScript developers.

How can the style/class of an element be changed?

It can be done in the following way:

Example

document.getElementById("myText").style.fontSize = "20

or

document.getElementById("myText").className = "anyclass";

What are all the looping structures in JavaScript?

For

While

do-while loops

What is called Variable typing in Javascript?

Variable typing is used to assign a number to a variable and the same variable can be assigned

to a string.

Example

i = 10;

i = "string";

What is the function of delete operator?

The functionality of delete operator is used to delete all variables and objects in a program but it

cannot delete variables declared with VAR keyword.

What are all the types of Pop up boxes available in JavaScript?

Alert

Confirm and

Prompt

What is the use of Void(0)?

Void(0) is used to prevent the page from refreshing and parameter "zero" is passed while calling.

Void(0) is used to call another method without refreshing the page.

How can a page be forced to load another page in JavaScript?

The following code has to be inserted to achieve the desired effect:

Example

<script language="JavaScript" type="text/javascript" >

<location.href="http://newhost/newpath/newfile.html";</script>

What is the difference between an alert box and a confirmation box?

An alert box displays only one button which is the OK button.

But a Confirmation box displays two buttons namely OK and cancel.

What are the different types of errors in JavaScript?

There are three types of errors:

Load time errors: Errors which come up when loading a web page like

improper syntax errors are known as Load time errors and it generates

the errors dynamically.

Run time errors: Errors that come due to misuse of the command inside

the HTML language.

Logical Errors: These are the errors that occur due to the bad logic

performed on a function which is having different operation.

Which keyword is used to print the text in the screen?

document.write("Welcome") is used to print the text - Welcome in the screen.

What is the use of blur function?

Blur function is used to remove the focus from the specified object.

What is the use of typeof operator?

'Typeof' is an operator which is used to return a string description of the type of a variable.

How to handle exceptions in JavaScript?

By using Try...Catch--finally keyword handle exceptions in the JavaScript

Example

try{code}catch(exp){code to throw an exception}finally{code runs either it finishes successfully or after catch

What is AngularJS ?

AngularJS is a javascript framework used for creating single web page applications.

What are the key features of Angularjs ?

Scope

Controller

Model

View

Services

Data Binding

Directives

Filters

Testable

What is scope in Angularjs ?

scope is an object that refers to the application model. It is an execution context for expressions.

Scopes are arranged in hierarchical structure which mimic the DOM structure of the application.

Scopes can watch expressions and propagate events.

What is controller in Angularjs ?

In Angular, a Controller is a JavaScript constructor function that is used to augment the Angular

Scope. When a Controller is attached to the DOM via the ng-controller directive, Angular will

instantiate a new Controller object, using the specified Controller's constructor function.

What is data binding in Angularjs ?

Data-binding in Angular apps is the automatic synchronization of data between the model and

view components.

What are the Advantages of using Angularjs

Two way data-binding

MVC pattern

Provides Static template and angular template

Can add custom directive

Provides REST full services

Provides form validations

Provides both client and server communication

Provides dependency injection

Applying Animations

Event Handlers

Read more......

Why called AngularJS ?

Because HTML has Angular brackets and "ng" sounds like "Angular".

AngularJS a library, framework, plugin or a browser extension?

AngularJS is the framework of JavaScript. AngularJS is 100% JavaScript, 100% client-side and

compatible with both desktop and mobile browsers. So it's definitely not a plugin or some other

native browser extension.

What are Directives?

At a high level, directives are markers on a DOM element (such as an attribute, element name,

comment or CSS class) that tell AngularJS's HTML compiler ($compile) to attach a specified

behavior to that DOM element or even transform the DOM element and its children.

Angular use the jQuery library?

Yes, Angular can use jQuery if it's present in your app when the application is being

bootstrapped. If jQuery is not present in your script path, Angular falls back to its own

implementation of the subset of jQuery that we call jQLite.

Why is this project called "AngularJS" ?

Because HTML has Angular brackets and "ng" sounds like "Angular".

Which browsers support Angular ?

AngularJS mostly support all new web browser, following browsers supported by angularJS:

Safari, Chrome, Firefox, Opera, IE8, IE9 and mobile browsers (Android, Chrome Mobile, iOS

Safari).

What are limitations of Angularjs ?

Not Secure: It is a framework of JavaScript not a server side

programming. Only server side programs provides security, server side

authentication and authorization provides security for application.

Depends on User: If any user disable JavaScript in their own browser

then nothing will be apply on your application related to JavaScript and

AngularJS, Only basic Html page will display.

What is ng-init directive ?

The ng-init directive initialize application data same like variable initialization in C language, In c

language you initialize int a=10;.

What is ng-model directive ?

The ng-model directive binds the value of HTML controls (input, select, textarea) to application

data. The ng-model directive defines the variable to be used in AngularJS Application.

What is ng-repeat directive ?

The ng-repeat directive repeats an Html element. ng-repeat directive repeats a specific

element. Read more......

What is expression in Ajgularjs ?

AngularJS Expressions used to binds application data to HTML. AngularJS expressions are

written inside double curly braces such as : {{ expression }}.

What is filter in Angularjs ?

Filter are mainly used for modify the data. Filters can be added to expressions and directives

using a pipe (|) character. For example uppercase filter are used for converting lower case text to

upper case text. Read more......

What is Angularjs Include ?

Using AngularJS, we can include or embed Html pages within an Html page using ng-include

directive. Read more......

How to define controller in angularjs ?

For define controller in AngularJS application we need ng-controller directive names. Read

more......

How to handel event in Angularjs ?

AngularJS have its own event directive to handle DOM events like mouse clicks, moves,

keyboard presses, change events etc. Read more......

MVC Architecture

What is MVC Architecture ?

MVC stand for Model View Controller. Model View Controller is a software design pattern for

developing web application. It given software application into three interconnected parts, model,

view and controller.

What is view in MVC ?

It is responsible for displaying output data to the user.

What is model in MVC ?

Model is responsible for maintaining data. Model retrieve data form database and also store data

in database.

What is Contoller in MVC ?

Controller It is responsible for controls the interactions between the Model and View. Controllers

can read data from a view, control user input, and send input data to the model. 

What is a class loader ?

Part of JVM which is used to load classes and interfaces.

What are the different class loaders used by JVM ?

Bootstrap , Extension and System are the class loaders used by JVM.

Different types of memory used by JVM ?

Class , Heap , Stack , Register , Native Method Stack.

What is the purpose of the System class ?

System class provide access to system resources.

Variable of the boolean type is automatically initialized as ?

The default value of the boolean type is false.

Difference between static vs. dynamic class loading ?

static loading: Classes are statically loaded with Java new operator.

dynamic class loading: Dynamic loading is a technique for programmatically invoking the

functions of a class loader at run time.

Difference between composition and inheritance in Java ?

Composition Inheritance

has-a relationship between classes. is-a relationship between classes.

Used in Dependency Injection Used in Runtime Polymorphism

Single class objects can be composed within multiple classes.

Single class can only inherit 1 Class.

Its the relationship between objects. Its the relationship between classes.

What do you mean by "Java is a statically typed language" ?

It means that the type of variables are checked at compile time in Java.The main advantage here

is that all kinds of checking can be done by the compiler and hence will reduce bugs.

What are different ways of object creation in Java ?

.

Using new operator - new xyzClass()

Using factory methods - xyzFactory.getInstance( )

Using newInstance( ) method

By cloning an already available object - (xyzClass)obj1.clone( )

Explain Autoboxing ?

Autoboxing is the automatic conversion that the Java compiler makes between the primitive types

and their corresponding object wrapper classes.

What is an Enum type ?

An enum type is a special data type that enables for a variable to be a set of predefined

constants.

What are Wrapper Classes ?

A wrapper class is any class which "wraps" or "encapsulates" the functionality of another class or

component.

What are Primitive Wrapper Classes ?

A Wrapper Class that wraps or encapsulates the primitive data type is called Primitive Wrapper

Class..

Why use Scanner class ?

For reading Data Stream from the input device.

Difference between loadClass and Class.forName ?

loadClass only loads the class but doesn't initialize the object whereas Class.forName initialize

the object after loading it.

Should we override finalize method ?

Finalize is used by Java for Garbage collection. It should not be done as we should leave the

Garbage Collection to Java itself.

Why Java don't use pointers ?

Pointers are vulnerable and slight carelessness in their use may result in memory problems and

hence Java intrinsically manage their use.

Do we need to import java.lang.package ?

No, It is loaded by default by the JVM.

What is the difference between System.out ,System.err and System.in ?

System.out and System.err both represent the monitor by default and hence can be used to send

data or results to the monitor. But System.out is used to display normal messages and results

whereas System.err is used to display error messages and System.in represents InputStream

object, which by default represents standard input device, i.e., keyboard.

Is it possible to compile and run a Java program without writing main( ) method ?

Yes, it is possible by using a static block in the Java program.

Can we call the garbage collector explicitly ?

We can call garbage collector of JVM to delete any unused variables and unreferenced objects

from memory using gc( ) method. This gc( ) method appears in both Runtime and System classes

of java.lang package.

What are different oops concept in java ?

OOPs stands for Object Oriented Programming. The oops concepts are similar in any other

programming languages. Because it is not programming concept. All oops concept in java are;

Class

Object

Polymorphism

Inheritance

Abstraction

Encapsulation

Aggreagation

Composition

Association

What is class ?

A class is a specification or blue print or template of an object.

What is object ?

Object is instance of class. It is dynamic memory allocation of class.

What are the Characteristics of Object ?

Characteristics of Object are;State Behavior and Identity.

Can a class extend more than one class in Java ?

No, a class can only extend another class because Java doesn't support multiple inheritances but

yes, it can implement multiple interfaces.

What is the difference between abstraction and polymorphism in Java ?

Abstraction generalizes the concept and Polymorphism allow you to use different implementation

without changing your code.

What is an Abstraction ?

Abstraction is a process to show only usful data and remaining hide from user.

Real Life Example of Abstraction ?

When you log into your email, compose and send a mail. Again there is a whole lot of

background processing involved, verifying the recipient, sending request to the email server,

sending your email. Here you are only interested in composing and clicking on the send button.

What really happens when you click on the send button, is hidden from you.

Real life example of abstraction ?

Real life example of abstraction is ATM machine; here only show balance in your account but not

display ATM pin code.

What is Encapsulation ?

The process of binding data and methods into a single unit is known as Encapsulation. In other

word The process of binding the data with related methods known as encapsulation.

Real Life Example of Encapsulation ?

Encapsulation is like enclosing in a capsule. 

Encapsulation is like your bag in which you can keep your pen, book etc.

What is inheritance ?

It is used in java for achieve concept of re-usability. As the name suggests , inheritance means to

take something that already made.

What is polymorphism ?

It is process to represent any things in multiple forms.

Real life example of Polymorphism ?

A Person who knows more than two languages he can speak in a language which he knows.

Here person is Object and speak is polymorphisam.

What is method overloading in Java ?

When same method is available in any class with same name and different signature is called

method overloading.

What is method overriding in Java ?

When same method available in base class and drive class with same name and same signature

it is called method overriding.

What is Aggregation ?

If a class have an entity reference, it is known as Aggregation. Aggregation represents HAS-A

relationship..

What is Composition ?

Composition is the design technique to implement has-a relationship in classes. Composition in

java is achieved by using instance variables that refers to other objects.

Can we declare abstract method as final ?

No. its not possible to declare abstract method with final keyword. Because abstract methods

should be override by its sub classes.

Is it possible to declare abstract method as private ?

No. its not possible to declare abstract method with private. Because abstract methods should be

override by its sub classes.

Differences between method Overloading and method Overriding ?

Overloaded Method Overridden Method

Arguments Must be Change Must not be change

Return Type Can change Can't change except for covariant

returns

Exceptions Can ChangeCan reduce or eliminate. Must not throw new or broader checked exceptions

Access Can change Must not make more restrictive (can be less restrictive)

InvocationReference type determines which overloaded version is selected. Happens at compile time.

Object type determines which method is selected. Happens at runtime.

Why use constructor ?

The main purpose of create a constructor is, for placing user defined values in place of default

values.

Why constructor not return any value ?

Constructor will never return any value even void, because the basic aim constructor is to place

value in the object

Why constructor definition should not be static ?

Constructor definition should not be static because constructor will be called each and every time

when object is created. If you made constructor is static then the constructor before object

creation same like main method.

Why constructor is not inherited ?

Constructor will not be inherited from one class to another class because every class constructor

is created for initialize its own data members.

What is purpose of default constructor ?

The purpose of default constructor is to create multiple object with respect to same class for

placing same value.

What is purpose of parameterized constructor ?

The purpose of parametrized constructor is to create multiple object with respect to same class

for placing different value of same type or different type or both.

Is constructor inherited?

No, constructor is not inherited.

Can you make a constructor final?

No, constructor can't be final.

What is the purpose of default constructor?

The default constructor provides the default values to the objects. The java compiler creates a

default constructor only if there is no constructor in the class.

Can we use both "this" and "super" in a constructor ?

No, because both this and super should be the first statement.

Does constructor return any value?

yes, that is current instance (You cannot use return type yet it returns a value).

What is flow of constructor in Java ?

Constructor are calling from bottom to top and executing from top to bottom.

Why overriding is not possible at constructor level. ?

The scope of constructor is within the class so that it is not possible to achieved overriding at

constructor level.

Difference between Method and Constructor

Method Constructor

1 Method can be any user defined name Constructor must be class name

2 Method should have return type It should not have any return type (even void)

3 Method should be called explicitly either with object reference or class reference

It will be called automatically whenever object is created

1 Method is not provided by compiler in any case.

The java compiler provides a default constructor if we do not have any constructor.

What is Abstraction ?

Abstraction is a process of hiding the implementation details and showing only functionality to the

user.

How achieve Abstraction in Java ?

There are two ways to achieve abstraction in java

Abstract class (0 to 100%)

Interface (100%)

Real life example of Abstraction ?

Mobile phone is one of example of abstraction. We only know about how to call and use mobile

but we can't know about internal functionally of mobile phone.

Real life example of Abstraction and Encapsulation ?

Outer Look of a Television, like it has a display screen and channel buttons to change channel it

explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen

are connect with each other using different circuits , it explains Encapsulation.

Which of the following Java feature show only important information ?

Inheritance

Encapsulation

Abstraction

Composition

Ans: Abstraction

What is Polymorphism ?

The ability to define a function in multiple forms is called Polymorphism.

What is Overloading ?

Whenever several methods have same names with;

Different method signature and different number or type of parameters.

Same method signature but different number of parameters.

Same method signature and same number of parameters but of different

type

It is determined at the compile time.

What is method overriding ?

If subclass (child class) has the same method as declared in the parent class, it is known as

method overriding in java. It is determined at the run time.

Difference between method overloading and mehtod Overloading ?

Method overloading is determined at the compile time and method overriding is determined at the

run time

How to achieve polymorphism in Java ?

How to achieve polymorphism in Java ?

In Java, static polymorphism is achieved through method overloading and method overriding.

Types of polymorphism in Java ?

In Java, there are two types of polymorphism.

Compile time polymorphism (static binding or method overloading)

Runtime polymorphism (dynamic binding or method overriding)

How to achieve static polymorphism in Java ?

In Java, static polymorphism is achieved through method overloading.

How to achieve dynamic polymorphism in Java ?

In Java, dynamic polymorphism is achieved through method overriding.

What is Compile time polymorphism ?

As the meaning is implicit, this is used to write the program in such a way, that flow of control is

decided in compile time itself. It is achieved using method overloading.

Example

public static int add(int a, int b){............}

public static double add(double a, double b){............}

public static float add(float a, float b){............}

What is Runtime polymorphism ?

Run time Polymorphism also known as method overriding and it is achieve at runtime.

Example

class Vehicle{ public void move() { System.out.println("Vehicles can move !!!!"); }}

class MotorBike extends Vehicle { public void move(){

System.out.println("MotorBike can move and accelerate too!!!");}}

class Demo {

public static void main(String[] args) { Vehicle obj=new MotorBike(); obj.move(); // prints message MotorBike can move and accelerate too!!! obj=new Vehicle(); obj.move(); // prints message Vehicles can move!! }}

What is Interface ?

An interface is a collection of abstract methods. A class implements an interface, thereby

inheriting the abstract methods of the interface..

Main features of Interface ?

Interface cannot be instantiated

An interface does not contain any constructors

All of the methods in an interface are abstract

Can an Interface be final ?

No, because its implementation is provided by another class.

What is marker interface ?

An interface that have no data member and method is known as a marker interface.For example

Serializable, Cloneable etc.

What is difference between abstract class and interface ?

An abstract class can have method body (non-abstract methods) but Interface have only abstract

methods.

How to implement Interface in Java ?

Syntax

interface A{........}interface B{........}class C implements A,B{........}

In Java Programming Inheritance is used for reuse features of one class into another class, Using

this concept enhance (improve or increase) performance of application.

What is Inheritance ?

Inheritance is one of the main features of any object oriented programming. Using inheritance

concept, a class (Sub Class) can inherit properties of another class (Super Class). So it is used

for reuse features.

Main advantage of using Inheritance ?

Using this feature you can reuse features, less memory wastage, less time required to develop

and application and improve performance of application.

Types of Inheritance supported by Java ?

Java support only four types of inheritance in java.

Single Inheritance

Multi level Inheritance

Hybrid Inheritance

Hierarchical Inheritance

Why use Inheritance ?

For Code Re usability.

For Method Overriding.

What is multilevel inheritance ?

Getting the properties from one class object to another class object level wise with different

priorities.

Which of these keyword must be used to inherit a class ?

a) super

b) this

c) extent

d) extends

d. extends

What is Multiple Inheritance ?

The concept of Getting the properties from multiple class objects to sub class object with same

priorities is known as multiple inheritance.

How Inheritance can be implemented in java ?

Inheritance can be implemented in Java using two keywords, they are;

extends

Implements

Which of these keywords is used to refer to member of base class from a sub class ?

a) upper

b) super

c) this

d) None of these

Answer: b

extends is used for developing inheritance between two classes and two interfaces.

Implements keyword is used to developed inheritance between interface and class.

What is syntax of inheritance ?

Syntax

public class subclass extends superclass{//all methods and variables declare here}

Which inheritance are not supported bb Java ?

Multi Inheritance is not supported by java.

How Inheritance can be implemented in java ?

Inheritance can be implemented in JAVA using these two keywords; extends and implements

How do you implement multiple inheritance in java ?

Using interfaces java can support multiple inheritance concept in java.

Syntax

interface A{........}interface B{........}class C implements A,B{........}

How do you implement multiple inheritance in java ?

Using interfaces java can support multiple inheritance concept in java. in java can not extend

more than one classes, but a class can implement more than one interfaces.

Why we need to use Inheritance ?

It is used for code re-usability and for Method Overriding.

Can a class extend itself ?

No, A class can't extend itself.

What is syntax of Inheritance ?

Syntax

public class subclass extends superclass{

//all methods and variables declare here}

Example of Single Inheritance in Java

Example

class Faculty{ float salary=30000; } class Science extends Faculty{ float bonous=2000;public static void main(String args[]){Science obj=new Science(); System.out.println("Salary is:"+obj.salary); System.out.println("Bonous is:"+obj.bonous); } }

why Java Doesn't Support multiple Inheritance ?

Due to ambiguity problem.

What happens if super class and sub class having same field name ?

Super class field will be hidden in the sub class. You can access hidden super class field in sub

class using super keyword.

How do you implement multiple inheritance in Java ?

Example

interface A{..........}interface B{..........}class C implements A,B{}

Can we reduce the visibility of the inherited or overridden method ?

Ans. No.

Which of the following is tightly bound ? Inheritance or Composition ?

Ans. Inheritance.

Does a class inherit the constructor of its super class ?

Ans. No