ECA 225 Applied Interactive Programming ECA 225 Applied Online Programming javascript dates

ECA 225 Applied Interactive Programming 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( );

ECA 225 Applied Interactive Programming 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

ECA 225 Applied Interactive Programming 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

ECA 225 Applied Interactive Programming 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 )

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getDay( )  returns the numeric day of the week, 0 – 6 var now = new Date( ); var d = now.getDay( ); // returns day of week alert( d )

ECA 225 Applied Interactive Programming Date( ) methods cont …  to return a string representation of the day of the week, use an array var now = new Date( ); var days = new Array( “Sunday”, “Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday”, “Saturday” ); alert( days[ now.getDay( ) ] ) ;

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getMonth( )  returns the numeric month, 0 – 11 var now = new Date( ); var month = now.getMonth( ); // returns month alert( month )

ECA 225 Applied Interactive Programming Date( ) methods cont …  to return a string representation of the month, use an array var now = new Date( ); var month = new Array( “January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December” ); alert( month[ now.getMonth( ) ] ) ;

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getFullYear( )  returns the numeric 4-digit year var now = new Date( ); var y4 = now.getFullYear( ); // returns 4-digit year alert( y4 )

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getYear( )  returns the numeric 2-digit year, pre-2000 var now = new Date( ); var y2 = now.getYear( ); // returns 2-digit year alert( y2 )

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getHours( )  returns the numeric hours, 0 – 23 var now = new Date( ); var h = now.getHours( ); // returns hours, 0 – 23 alert( h )

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getMinutes( )  returns the numeric minutes, 0 – 59 var now = new Date( ); var m = now.getMinutes( ); // returns hours, 0 – 59 alert( m )

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getSeconds( )  returns the numeric seconds, 0 – 59 var now = new Date( ); var s = now.getSeconds( ); // returns seconds, 0 – 59 alert( s )

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getMilliseconds( )  returns the numeric milliseconds, 0 – 999 var now = new Date( ); var ms = now.getMilliseconds( ); // returns 0 – 999 alert( ms )

ECA 225 Applied Interactive Programming 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

ECA 225 Applied Interactive Programming Greenwich Mean Time GMT Uzbekistan +5 Ohio – 5 IDL

ECA 225 Applied Interactive Programming GMT / UTC  another name for GMT is UTC, Coordinated Universal Time  many JavaScript methods have 2 versions  one for local time  one for GMT or UTC

ECA 225 Applied Interactive Programming milliseconds  basic unit of measuring JavaScript time is one millisecond, or 1/1000 th 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

ECA 225 Applied Interactive Programming Date( ) methods cont …  Date.getTime( )  returns the number of milliseconds since the Unix Epoch, midnight, 1 January, 1970 var now = new Date( ); var ts = now.getTime( ); // returns the number // of milliseconds since midnight, 1 Jan, 1970 alert( ts )

ECA 225 Applied Interactive Programming 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

ECA 225 Applied Interactive Programming 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 );

ECA 225 Applied Interactive Programming  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 :00:00 “ );

ECA 225 Applied Interactive Programming 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 );

ECA 225 Applied Interactive Programming 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 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setMonth( )  set the month, given a number between 0 – 11 var date1 = new Date( ); alert ( date1 ); date1.setMonth( 3 ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setFullYear( )  set the year, given a 4 digit year var date1 = new Date( ); alert ( date1 ); date1.setFullYear( 2013 ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setYear( )  set the year, given a 2 or 4 digit year var date1 = new Date( ); alert ( date1 ); date1.setYear( 2013 ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setHours( )  set the hour, given a number between 0 – 23 var date1 = new Date( ); alert ( date1 ); date1.setHour( 13 ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setMinutes( )  set the minutes, given a number between 0 – 59 var date1 = new Date( ); alert ( date1 ); date1.setMinutes( 33 ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setSeconds( )  set the seconds, given a number between 0 – 59 var date1 = new Date( ); alert ( date1 ); date1.setSeconds( 33 ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setMilliseconds( )  set the milliseconds, given a number between 0 – 999 var date1 = new Date( ); alert ( date1 ); date1.setMilliseconds( 613 ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  Date.setTime( )  set a date, given the number of milliseconds since 1 January 1970 var date1 = new Date( ); alert ( date1 ); date1.setTime( ); alert ( date1 );

ECA 225 Applied Interactive Programming Date( ) set methods cont …  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 );

ECA 225 Applied Interactive Programming 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

ECA 225 Applied Interactive Programming 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;

ECA 225 Applied Interactive Programming.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

ECA 225 Applied Interactive Programming.js library cont …  the reference to the external.js file will look like:  the tag MUST have a corresponding closing tag  avoid putting any other code inside the opening and closing tags  place reference inside tags

ECA 225 Applied Interactive Programming.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 code  do not place any confidential or sensitive material inside a.js file

ECA 225 Applied Interactive Programming 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 );

ECA 225 Applied Interactive Programming 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 );