How to search for multiple index(es) of same values in javascript array

Question

I have a 1 dimensional array like:

var abc = ['a','a','b','a','c']

Now I want to get back all the indexes of 'a', that is 0, 1 and 3.

Are there any simple solutions?

P.S.

I know IndexOf or jQuery.inArray(). But they just returned the index of first matched element only

Answer 1

You could extend the basic Array Object with the following method:

Array.prototype.multiIndexOf = function (el) { 
    var idxs = [];
    for (var i = this.length - 1; i >= 0; i--) {
        if (this[i] === el) {
            idxs.unshift(i);
        }
    }
    return idxs;
};

Then the operation

var abc = ['a','a','b','a','c'];
abc.multiIndexOf('a');

would give you the result:

[0, 1, 3]

Jsperf comparison of unshift / push / push(reverse order)

Answer 2

You can take advantage of the fact that $.map() does not push values in its resulting array when the function you pass returns undefined.

Therefore, you can write:

var abc = ["a", "a", "b", "a", "c"];
var indices = $.map(abc, function(element, index) {
    if (element == "a") {
        return index;
    }
});