Compare two dates with JavaScript

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Top 5 Answer for Compare two dates with JavaScript

vote vote

95

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.


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.)

vote vote

80

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         );     } } 
vote vote

72

Compare < and > just as usual, but anything involving == or === should use a + prefix. Like so:

const x = new Date('2013-05-23'); const y = new Date('2013-05-23');  // less than, greater than is fine: console.log('x < y', x < y); // false console.log('x > y', x > y); // false console.log('x <= y', x <= y); // true console.log('x >= y', x >= y); // true console.log('x === y', x === y); // false, oops!  // anything involving '==' or '===' should use the '+' prefix // it will then compare the dates' millisecond values  console.log('+x === +y', +x === +y); // true

vote vote

66

The relational operators < <= > >= can be used to compare JavaScript dates:

var d1 = new Date(2013, 0, 1); var d2 = new Date(2013, 0, 2); d1 <  d2; // true d1 <= d2; // true d1 >  d2; // false d1 >= d2; // false 

However, the equality operators == != === !== cannot be used to compare (the value of) dates because:

  • Two distinct objects are never equal for either strict or abstract comparisons.
  • An expression comparing Objects is only true if the operands reference the same Object.

You can compare the value of dates for equality using any of these methods:

var d1 = new Date(2013, 0, 1); var d2 = new Date(2013, 0, 1); /*  * note: d1 == d2 returns false as described above  */ d1.getTime() == d2.getTime(); // true d1.valueOf() == d2.valueOf(); // true Number(d1)   == Number(d2);   // true +d1          == +d2;          // true 

Both Date.getTime() and Date.valueOf() return the number of milliseconds since January 1, 1970, 00:00 UTC. Both Number function and unary + operator call the valueOf() methods behind the scenes.

vote vote

52

By far the easiest method is to subtract one date from the other and compare the result.

var oDateOne = new Date();  var oDateTwo = new Date();    alert(oDateOne - oDateTwo === 0);  alert(oDateOne - oDateTwo < 0);  alert(oDateOne - oDateTwo > 0);

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