How to fix Array indexOf() in JavaScript for Inter

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() [including Internet Explorer 8]. It is not a huge problem, because you can extend the functionality on your page with the following code.

Array.prototype.indexOf = function(obj, start) {
     for (var i = (start || 0), j = this.length; i < j; i++) {
         if (this[i] === obj) { return i; }
     }
     return -1;
}

When should I implement this?

Should I wrap it on all my pages with the following check, which checks if the prototype function exists and if not, go ahead and extend the Array prototype?

if (!Array.prototype.indexOf) {

    // Implement function here

}

Or do browser check and if it is Internet Explorer then just implement it?

//Pseudo-code

if (browser == IE Style Browser) {

     // Implement function here

}

Answer 1

With the Underscore.js

var arr=['a','a1','b'] _.filter(arr, function(a){ return a.indexOf('a') > -1; })

Answer 2

Do it like this...

if (!Array.prototype.indexOf) {

}

As recommended compatibility by MDC.

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

Answer 3

The full code then would be this:

if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function(obj, start) {
         for (var i = (start || 0), j = this.length; i < j; i++) {
             if (this[i] === obj) { return i; }
         }
         return -1;
    }
}

For a really thorough answer and code to this as well as other array functions check out Stack Overflow question Fixing JavaScript Array functions in Internet Explorer (indexOf, forEach, etc.).

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;
        };
    }
})();