Why Does `Array.indexOf()` Fail in IE8, and How Can It Be Fixed?

Array.indexOf() Function Fails in IE8

The indexOf() function, used to check the index of an element in an array, presents challenges in Internet Explorer (IE) versions prior to 9. Specifically, in IE8, this function doesn't work as expected, leaving developers stumped.

To trace the root cause, consider the following function, which is functional in browsers such as Opera, Firefox, and Chrome:

function CheckMe() {
    var allowed = new Array('docx','xls','xlsx', 'mp3', 'mp4', '3gp', 'sis', 'sisx', 'mp3', 'wav', 'mid', 'amr', 'jpg', 'gif', 'png', 'jpeg', 'txt', 'pdf', 'doc', 'rtf', 'thm', 'rar', 'zip', 'htm', 'html', 'css', 'swf', 'jar', 'nth', 'aac', 'cab', 'wgz');
    var fileinput=document.getElementById('f');
    var ext = fileinput.value.toLowerCase().split('.');
    
    if (allowed.indexOf(ext[1]) == -1) {...

The error occurs when the function attempts to execute the if (allowed.indexOf(ext[1]) == -1) conditional statement. In IE8, indexOf() is not supported for arrays, causing the code to fail.

To rectify this issue, the following fix can be implemented:

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 fix adds the indexOf() method to the Array prototype if it's not present, specifically targeting IE8 or below where it's missing. By incorporating this fix, the CheckMe() function would perform as intended, resolving the issue in IE8.

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