Question

49

How to correctly use JavaScript indexOf in a date array

rated 0 times [ 52] [ 3] / answers: 1 / hits: 20200 / 10 Years ago, fri, december 12, 2014, 12:00:00

Here is the code:

var collection = [new Date(2014, 11, 25), new Date(2014, 11, 24)];

var d=new Date(2014, 11, 24);



var idx= collection.indexOf(d);

I guess the variable idx should have a value of 1 since it is the second value in the array collection. But it turns out to be -1.

Why is that? Is there any special thing for the JavaScript Date type I need to pay attention?

Here is a snippet:

(function() {



  var collection = [new Date(2014, 11, 25), new Date(2014, 11, 24)];

  var d = new Date(2014, 11, 24);



  var idx1 = collection.indexOf(d);



  var intArray = [1, 3, 4, 5];

  var idx2 = intArray.indexOf(4);



  $('#btnTry1').on('click', function() {

    $('#result1').val(idx1);

  });



  $('#btnTry2').on('click', function() {

    $('#result2').val(idx2);

  });

})();

<script src=https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js></script>

Index:

<input type=text id=result1 value=>

<button id=btnTry1>Find index in a date array</button>

<br />Index:

<input type=text id=result2 value=>

<button id=btnTry2>Find index in a regular array</button>

Answers

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chyanne

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2 Years ago

answered 10 Years ago yaquelina · Accepted Answer

Two Objects will never be equal unless you serialise them. Lucky, Date is pretty easy to serialise as an integer.

var collection = [new Date(2014, 11, 25), new Date(2014, 11, 24)],

    d = new Date(2014, 11, 24),

    idx;



idx = collection.map(Number).indexOf(+d); // 1

//              ^^^^^^^^^^^^         ^ serialisation steps