ECA 225

ECA 225 Applied Interactive Programming

ECA 225AppliedOnline

Programming

javascript dates


Date( ) constructor

to create a new Date object use the new operator

this instance of a Date( ) object contains the current date and time, the exact date and time, to the millisecond, it was created var now = new Date( );


Date( ) constructor cont …

if we use the alert( ) method to display the current date

we get a value similar to: var now = new Date( );alert( now );

Thu Sep 25 15:28:20 EDT 2003


Date( ) methods

the Date( ) object can be broken down into its individual pieces using a variety of Date( ) methods

because the variable name we created ( now ) holds a reference to a Date( ) object, we can use dot notation to access methods


Date( ) methods cont …

Date.getDate( ) returns the numeric day of the month

var now = new Date( );

var d = now.getDate( ); // returns day of month

alert( d )



Date.getDay( ) returns the numeric day of the week, 0 – 6


var d = now.getDay( ); // returns day of week

alert( d )



to return a string representation of the day of the week, use an array


var days = new Array( “Sunday”, “Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday”, “Saturday” );

alert( days[ now.getDay( ) ] ) ;



Date.getMonth( ) returns the numeric month, 0 – 11


var month = now.getMonth( ); // returns month

alert( month )



to return a string representation of the month, use an array


var month = new Array( “January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December” );

alert( month[ now.getMonth( ) ] ) ;



Date.getFullYear( ) returns the numeric 4-digit year


var y4 = now.getFullYear( ); // returns 4-digit year

alert( y4 )



Date.getYear( ) returns the numeric 2-digit year, pre-2000


var y2 = now.getYear( ); // returns 2-digit year

alert( y2 )



Date.getHours( ) returns the numeric hours, 0 – 23


var h = now.getHours( ); // returns hours, 0 – 23

alert( h )



Date.getMinutes( ) returns the numeric minutes, 0 – 59


var m = now.getMinutes( ); // returns hours, 0 – 59

alert( m )



Date.getSeconds( ) returns the numeric seconds, 0 – 59


var s = now.getSeconds( ); // returns seconds, 0 – 59

alert( s )



Date.getMilliseconds( ) returns the numeric milliseconds, 0 – 999


var ms = now.getMilliseconds( ); // returns 0 – 999

alert( ms )


local time

the date and time to which a Date( ) object is set is based upon the local time of the user’s computer, not the server

scripts read the clock setting of the user’s computer

to make time comparisons between a user’s local time and another time zone a standard reference point is needed


Greenwich Mean Time GMT

Uzbekistan+5

Ohio– 5

IDL


GMT / UTC

another name for GMT is UTC, Coordinated Universal Time

many JavaScript methods have 2 versionsone for local timeone for GMT or UTC


milliseconds

basic unit of measuring JavaScript time is one millisecond, or 1/1000th of a second

JavaScript maintains date information in the form of a count, in milliseconds, since 1 January, 1970, at midnight, in Greenwich, England

midnight, 1 January, 1970 is known as the Unix Epoch



Date.getTime( ) returns the number of milliseconds since the Unix

Epoch, midnight, 1 January, 1970


var ts = now.getTime( ); // returns the number

// of milliseconds since midnight, 1 Jan, 1970

alert( ts )


comparing Date( ) objects

to compare different Date( ) objects, return the number of milliseconds that have passed for each, since the Unix Epoch

compare the milliseconds – the one which is smaller in size occurred first


creating Date( ) objects

to create Date( ) object to a specific day and time, such as a future date

new Date( “Month dd, yyyy hh:mm:ss “ ); new Date( “Month dd, yyyy” ); new Date( yy,mm,dd,hh,mm,ss ); new Date( yy,mm,dd ); new Date( milliseconds );


to create a Date( ) object holding the values for New Year’s Day, midnight, 2013

creating Date( ) objects cont …

var newYear = new Date(2013,00,01,00,00,00)

var newYear = new Date( “January 1 2013 00:00:00 “ );


Date( ) set methods JavaScript’s Date( ) set methods are used to set

or reset the values associated with the object

set methods return the new date in milliseconds

var date1 = new Date( );alert ( date1 );date1.setFullYear( 2007 );alert ( date1 );


Date( ) set methods cont …

Date.setDate( ) set the day, given a number between 1 – 31

var date1 = new Date( );alert ( date1 );date1.setDate( 13 );alert ( date1 );



Date.setMonth( ) set the month, given a number between 0 – 11

var date1 = new Date( );alert ( date1 );date1.setMonth( 3 );alert ( date1 );



Date.setFullYear( ) set the year, given a 4 digit year

var date1 = new Date( );alert ( date1 );date1.setFullYear( 2013 );alert ( date1 );



Date.setYear( ) set the year, given a 2 or 4 digit year

var date1 = new Date( );alert ( date1 );date1.setYear( 2013 );alert ( date1 );



Date.setHours( ) set the hour, given a number between 0 – 23

var date1 = new Date( );alert ( date1 );date1.setHour( 13 );alert ( date1 );



Date.setMinutes( ) set the minutes, given a number between 0 – 59

var date1 = new Date( );alert ( date1 );date1.setMinutes( 33 );alert ( date1 );



Date.setSeconds( ) set the seconds, given a number between 0 – 59

var date1 = new Date( );alert ( date1 );date1.setSeconds( 33 );alert ( date1 );



Date.setMilliseconds( ) set the milliseconds, given a number between 0 – 999

var date1 = new Date( );alert ( date1 );date1.setMilliseconds( 613 );alert ( date1 );



Date.setTime( ) set a date, given the number of milliseconds since

1 January 1970

var date1 = new Date( );alert ( date1 );date1.setTime(1036090020000 );alert ( date1 );



a construction used to set a Date( ) object to a specific distance in the future:

var date1 = new Date( );alert ( date1 );date1.setFullYear( date1.getFullYear( ) + 1 );alert ( date1 );


Date & Time Arithmetic

the millisecond is the JavaScript basic unit of time

precise time calculations involving the addition or subtraction of dates should be performed using milliseconds


Date & Time Arithmetic cont … creation of variables holding the number of

milliseconds in a minute, hour, day and week may be useful

var one_minute = 60 * 1000;var one_hour = one_minute * 60;var one_day = one_hour * 24;var one_week = one_day * 7;


.js library

the previous variables, plus the arrays holding the names of the days and months, can be placed in an external JavaScript file

the external file, or library, can then be referenced by any page, similar to an external style sheet

external files must end with a .js extension


.js library cont … the reference to the external .js file will look like:

the <script> tag MUST have a corresponding closing </script> tag

avoid putting any other code inside the opening and closing <script> tags

place reference inside <head> tags

<script type=‘text/javascript’ href=‘path_to_js_file.js’ ></script>


.js library cont …

the server must be configured correctly to serve an external .js file

CAUTION: using an external .js file does not hide your codedo not place any confidential or sensitive material

inside a .js file


Date & Time Arithmetic cont … EG, to create a date exactly 26 weeks from the

current date:

var date1 = new Date( );alert ( date1 );date1.setTime( date1.getTime( ) + one_week * 26 );alert ( date1 );


Date & Time Arithmetic cont … to set the expiration date for a cookie to 6

months hence

or

var exp = new Date( );exp.setTime( exp.getTime( ) + one_week * 26 );

var exp = new Date( );exp.setMonth( exp.getMonth( ) + 6 );

ECA 225

Documents

new date eca

new date var month

new date alert

new date var y4

new date var y2

new date var s

new date var h

new date var ms