How to correctly use JavaScript indexOf in a date array

Question

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);

Answer 1

Two different objects are never equal to each other, even if they have the same properties / values. Here is a forward looking answer to the problem:

ECMAScript 6 introduces Array#findIndex which accepts a comparison callback:

var index = collection.findIndex(function(x) { 
    return x.valueOf() === d.valueOf(); 
});

Browser support isn't great yet though.