Date Functions

by dnviti

HTML

<label for="date">Date</label>
<input type="date" name="date" id="date" style="width:130px;text-align:center" value="" />
<br /><br />
<label for="year">Year</label>
<input type="year" name="year" id="year" style="width:40px;text-align:center" value="" />
-
<label for="week">Week</label>
<input type="text" id="week" style="width:25px;text-align:center" value="" />
<br /><br />
<label for="fullDate">Full Date</label>
<input type="text" id="fullDate" name="fullDate" style="width:80px;text-align:center" value="" />
<br /><br />
<button id="convertToDate">
Convert Date
</button>

CSS

*{
  font-family: consolas
}

JavaScript

/** 
 * Get the ISO week date week number 
 */  
Date.prototype.getWeek = function () {  
  // Create a copy of this date object  
  var target  = new Date(this.valueOf());  

  // ISO week date weeks start on monday  
  // so correct the day number  
  var dayNr   = (this.getDay() + 6) % 7;  

  // ISO 8601 states that week 1 is the week  
  // with the first thursday of that year.  
  // Set the target date to the thursday in the target week  
  target.setDate(target.getDate() - dayNr + 3);  

  // Store the millisecond value of the target date  
  var firstThursday = target.valueOf();  

  // Set the target to the first thursday of the year  
  // First set the target to january first  
  target.setMonth(0, 1);  
  // Not a thursday? Correct the date to the next thursday  
  if (target.getDay() != 4) {  
    target.setMonth(0, 1 + ((4 - target.getDay()) + 7) % 7);  
  }  

  // The weeknumber is the number of weeks between the   
  // first thursday of the year and the thursday in the target week  
  return 1 + Math.ceil((firstThursday - target) / 604800000); // 604800000 = 7 * 24 * 3600 * 1000  
}  

/** 
* Get the ISO week date year number 
*/  
Date.prototype.getWeekYear = function ()   
{  
  // Create a new date object for the thursday of this week  
  var target  = new Date(this.valueOf());  
  target.setDate(target.getDate() - ((this.getDay() + 6) % 7) + 3);  

  return target.getFullYear();  
}

/** 
 * Convert ISO week number and year into date (first day of week)
 */ 
var getDateFromISOWeek = function(w, y) {
  var simple = new Date(y, 0, 1 + (w - 1) * 7);
  var dow = simple.getDay();
  var ISOweekStart = simple;
  if (dow <= 4)
    ISOweekStart.setDate(simple.getDate() - simple.getDay() + 1);
  else
    ISOweekStart.setDate(simple.getDate() + 8 - simple.getDay());
  return ISOweekStart;
}

var printDate = function(){
  /*var dateString = document.getElementById("date").value;
	var dateArray = dateString.split("/");*/ // use this if you have...