Conditionals

Conditionalsforks in the road

Tuesday, September 22, 2009




if statementexecute some code only if a statement is true

http://www.w3schools.com/JS/js_if_else.asp




if


if (conditional)


if (conditional) {


if (conditional) { // statement to be executed


if (conditional) { // statement to be executed}


truefalse


var age = 60;var status = null;

if (age > 62) { status = 'retired';}

status; // null




status; // null

60 > 62 === false

this never executes

so status is never assigned and remains null




status; // "retired"





65 > 62 === true

this executes

so status is set to “retired”


if...else statementexecute some code if statement is true

and some other code if statement is falsehttp://www.w3schools.com/JS/js_if_else.asp




if (conditional) { // statement if true}


if (conditional) { // statement if true} else


if (conditional) { // statement if true} else {


if (conditional) { // statement if true} else { // statement if false


if (conditional) { // statement if true} else { // statement if false}


truefalse



if (age > 62) { status = 'retired';} else { status = 'not retired';}

status; // "not retired"



if (age > 62) { status = 'retired';} else { status = 'not retired';}



if...else if...else statementexecute some code if statement is true

and some other code if statement is falsehttp://www.w3schools.com/JS/js_if_else.asp




if (conditional) { // statement if true} else if (conditional) { // statement if false and else if true} else { // statement if all false}


if (conditional) { // statement if true} else if (conditional) { // whichever matches first} else if (conditional) { // whichever matches first} else if (conditional) { // whichever matches first} else { // statement if all false}



if (age >= 62) { status = 'retired';} else if (age > 22 && age < 62) { status = 'working';} else if (age >= 18 && age <= 22) { status = 'college';} else { status = 'no responsibilities';}

status;


switch statementselect one of many blocks of code to execute

http://www.w3schools.com/JS/js_switch.asp




switch


switch (value)


switch (value) {


switch (value) { case 1:


switch (value) { case 1: // some code to execute


switch (value) { case 1: // some code to execute break;


switch (value) { case 1: // some code to execute break; case 2: // some code to execute break;


switch (value) { case 1: // some code to execute break; case 2: // some code to execute break; default: // nothing matched so do this


switch (value) { case 1: // some code to execute break; case 2: // some code to execute break; default: // nothing matched so do this

similar to else in if...else


switch (value) { case 1: // some code to execute break; case 2: // some code to execute break; default: // nothing matched so do this}


var age = 18;

switch (typeof(age)) { case 'number': "I'm a number!"; break; case 'string': "I'm a string!"; break; case 'boolean': "I'm a boolean!"; break; default: "I don't know what I am!";}

// "I'm a number!"Tuesday, September 22, 2009

for(action in json) { var selectors = json[action]; switch(action) { case 'replace' : for(selector in selectors) $(selector).html(selectors[selector]); break; case 'append' : for(selector in selectors) $(selector).append(selectors[selector]); break; case 'prepend' : for(selector in selectors) $(selector).prepend(selectors[selector]); break; case 'replaceWith' : for(selector in selectors) $(selector).replaceWith(selectors[selector]); break; case 'insertBefore' : for(selector in selectors) $(selectors[selector]).insertBefore($(selector)); break; case 'sidebar' : Sidebar.add(selectors); break; case 'remove' : $(selectors.join(',')).remove(); break; }}


Review


var age = 18;var teens = false;

if (age > 12 && age < 20) { teens = true;}

teens;


var age = 18;var teens = false;

if (age > 12 && age < 20) { teens = true;}

teens; // true


var days = ['sunday', 'monday', 'tuesday'];var first = days[0];var week_starts_on_sunday = false;

if (first === 'sunday') { week_starts_on_sunday = true;}

week_starts_on_sunday;


var days = ['sunday', 'monday', 'tuesday'];var first = days[0];var week_starts_on_sunday = false;


week_starts_on_sunday; // true


var days = ['monday', 'tuesday', 'sunday'];var first = days[0];var week_starts_on_sunday = false;


week_starts_on_sunday;


var days = ['monday', 'tuesday', 'sunday'];var first = days[0];var week_starts_on_sunday = false;


week_starts_on_sunday; // false


Assignmenthttp://teaching.johnnunemaker.com/capp-30550/sessions/conditionals


http://teaching.johnnunemaker.com/capp-30550/sessions/conditionals

http://teaching.johnnunemaker.com/capp-30550/sessions/conditionals

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true tuesday

false true

false http

age lt

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statement

false tuesday

age gt