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ECA 225

ECA 225. Applied Online 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( );.

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ECA 225

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  1. ECA 225 AppliedOnline Programming javascript dates ECA 225 Applied Interactive Programming

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

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

  18. 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

  19. 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 ECA 225 Applied Interactive Programming

  20. 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

  21. 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

  22. 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

  23. creating Date( ) objects cont … • to create a Date( ) object holding the values for New Year’s Day, midnight, 2013 var newYear = new Date(2013,00,01,00,00,00) var newYear = new Date( “January 1 2013 00:00:00 “ ); ECA 225 Applied Interactive Programming

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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(1036090020000 );alert ( date1 ); ECA 225 Applied Interactive Programming

  34. 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

  35. 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

  36. 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

  37. .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

  38. .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> ECA 225 Applied Interactive Programming

  39. .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

  40. 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

  41. 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 Applied Interactive Programming

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