How to fix Array indexOf() in JavaScript for Internet Explorer browsers

Question

If you have worked with JavaScript at any length you are aware that Internet Explorer does not implement the ECMAScript function for Array.prototype.indexOf() [includin

Answer 1

You should check if it's not defined using if (!Array.prototype.indexOf).

Also, your implementation of indexOf is not correct. You must use === instead of == in your if (this[i] == obj) statement, otherwise [4,"5"].indexOf(5) would be 1 according to your implementation, which is incorrect.

I recommend you use the implementation on MDC.

Answer 2

I would recommend this to anyone looking for missing functionality:

http://code.google.com/p/ddr-ecma5/

It brings in most of the missing ecma5 functionality to older browers :)

Answer 3

The underscore.js library has an indexOf function you can use instead:

_.indexOf([1, 2, 3], 2)

Answer 4

There is Mozilla official solution: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf

(function() {
    /**Array*/
    // Production steps of ECMA-262, Edition 5, 15.4.4.14
    // Reference: http://es5.github.io/#x15.4.4.14
    if (!Array.prototype.indexOf) {
        Array.prototype.indexOf = function(searchElement, fromIndex) {
            var k;
            // 1. Let O be the result of calling ToObject passing
            //    the this value as the argument.
            if (null === this || undefined === this) {
                throw new TypeError('"this" is null or not defined');
            }
            var O = Object(this);
            // 2. Let lenValue be the result of calling the Get
            //    internal method of O with the argument "length".
            // 3. Let len be ToUint32(lenValue).
            var len = O.length >>> 0;
            // 4. If len is 0, return -1.
            if (len === 0) {
                return -1;
            }
            // 5. If argument fromIndex was passed let n be
            //    ToInteger(fromIndex); else let n be 0.
            var n = +fromIndex || 0;
            if (Math.abs(n) === Infinity) {
                n = 0;
            }
            // 6. If n >= len, return -1.
            if (n >= len) {
                return -1;
            }
            // 7. If n >= 0, then Let k be n.
            // 8. Else, n<0, Let k be len - abs(n).
            //    If k is less than 0, then let k be 0.
            k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);
            // 9. Repeat, while k < len
            while (k < len) {
                // a. Let Pk be ToString(k).
                //   This is implicit for LHS operands of the in operator
                // b. Let kPresent be the result of calling the
                //    HasProperty internal method of O with argument Pk.
                //   This step can be combined with c
                // c. If kPresent is true, then
                //    i.  Let elementK be the result of calling the Get
                //        internal method of O with the argument ToString(k).
                //   ii.  Let same be the result of applying the
                //        Strict Equality Comparison Algorithm to
                //        searchElement and elementK.
                //  iii.  If same is true, return k.
                if (k in O && O[k] === searchElement) {
                    return k;
                }
                k++;
            }
            return -1;
        };
    }
})();

Answer 5

it works for me.

if (!Array.prototype.indexOf) {
  Array.prototype.indexOf = function(elt /*, from*/) {
    var len = this.length >>> 0;

    var from = Number(arguments[1]) || 0;
    from = (from < 0)? Math.ceil(from) : Math.floor(from);
    if (from < 0)
    from += len;

    for (; from < len; from++) {
      if (from in this && this[from] === elt)
        return from;
    }
    return -1;
  };
}

Answer 6

Do it like this...

if (!Array.prototype.indexOf) {

}

As recommended compatibility by MDC.

In general, browser detection code is a big no-no.