Compare two dates with JavaScript

Question

Can someone suggest a way to compare the values of two dates greater than, less than, and not in the past using JavaScript? The values will be coming from text boxes.

Answer 1

The Date object will do what you want - construct one for each date, then compare them using the >, <, <= or >=.

The ==, !=, ===, and !== operators require you to use date.getTime() as in

var d1 = new Date(); var d2 = new Date(d1); var same = d1.getTime() === d2.getTime(); var notSame = d1.getTime() !== d2.getTime(); 

to be clear just checking for equality directly with the date objects won't work

var d1 = new Date(); var d2 = new Date(d1);  console.log(d1 == d2);   // prints false (wrong!)  console.log(d1 === d2);  // prints false (wrong!) console.log(d1 != d2);   // prints true  (wrong!) console.log(d1 !== d2);  // prints true  (wrong!) console.log(d1.getTime() === d2.getTime()); // prints true (correct) 

I suggest you use drop-downs or some similar constrained form of date entry rather than text boxes, though, lest you find yourself in input validation hell.

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For the curious, date.getTime() documentation:

Returns the numeric value of the specified date as the number of milliseconds since January 1, 1970, 00:00:00 UTC. (Negative values are returned for prior times.)

Answer 2

The easiest way to compare dates in javascript is to first convert it to a Date object and then compare these date-objects.

Below you find an object with three functions:

• dates.compare(a,b)

  Returns a number:

  • -1 if a < b
  • 0 if a = b
  • 1 if a > b
  • NaN if a or b is an illegal date

• dates.inRange (d,start,end)

  Returns a boolean or NaN:

  • true if d is between the start and end (inclusive)
  • false if d is before start or after end.
  • NaN if one or more of the dates are illegal.

• dates.convert

  Used by the other functions to convert their input to a date object. The input can be

  • a date-object : The input is returned as is.
  • an array: Interpreted as [year,month,day]. NOTE month is 0-11.
  • a number : Interpreted as number of milliseconds since 1 Jan 1970 (a timestamp)
  • a string : Several different formats is supported, like "YYYY/MM/DD", "MM/DD/YYYY", "Jan 31 2009" etc.
  • an object: Interpreted as an object with year, month and date attributes. NOTE month is 0-11.

.

// Source: http://stackoverflow.com/questions/497790 var dates = {     convert:function(d) {         // Converts the date in d to a date-object. The input can be:         //   a date object: returned without modification         //  an array      : Interpreted as [year,month,day]. NOTE: month is 0-11.         //   a number     : Interpreted as number of milliseconds         //                  since 1 Jan 1970 (a timestamp)          //   a string     : Any format supported by the javascript engine, like         //                  "YYYY/MM/DD", "MM/DD/YYYY", "Jan 31 2009" etc.         //  an object     : Interpreted as an object with year, month and date         //                  attributes.  **NOTE** month is 0-11.         return (             d.constructor === Date ? d :             d.constructor === Array ? new Date(d[0],d[1],d[2]) :             d.constructor === Number ? new Date(d) :             d.constructor === String ? new Date(d) :             typeof d === "object" ? new Date(d.year,d.month,d.date) :             NaN         );     },     compare:function(a,b) {         // Compare two dates (could be of any type supported by the convert         // function above) and returns:         //  -1 : if a < b         //   0 : if a = b         //   1 : if a > b         // NaN : if a or b is an illegal date         // NOTE: The code inside isFinite does an assignment (=).         return (             isFinite(a=this.convert(a).valueOf()) &&             isFinite(b=this.convert(b).valueOf()) ?             (a>b)-(a<b) :             NaN         );     },     inRange:function(d,start,end) {         // Checks if date in d is between dates in start and end.         // Returns a boolean or NaN:         //    true  : if d is between start and end (inclusive)         //    false : if d is before start or after end         //    NaN   : if one or more of the dates is illegal.         // NOTE: The code inside isFinite does an assignment (=).        return (             isFinite(d=this.convert(d).valueOf()) &&             isFinite(start=this.convert(start).valueOf()) &&             isFinite(end=this.convert(end).valueOf()) ?             start <= d && d <= end :             NaN         );     } }