Why is my JavaScript `indexOf()` method failing in IE8, and how can I fix it?

Missing Array indexOf() Method in IE8

In the provided code, the indexOf() method is used on an array within the CheckMe() function. While this function works flawlessly in Opera, Firefox, and Chrome, it encounters an error in IE8 at the line if ( allowed.indexOf(ext[1]) == -1). This issue arises because IE8 does not natively support the indexOf() function for arrays.

To resolve this issue, you can incorporate a polyfill that adds the indexOf() method to the Array object. Here's an example:

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;
  };
}

This implementation of indexOf() is based on the version from MDN and is compatible with Firefox and SpiderMonkey. It will add the indexOf() method to the Array object in IE8 or any other browser that does not natively support it.

By incorporating this polyfill, you can ensure that your code will function as intended even in legacy browsers like IE8 that lack the indexOf() method.

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