How Can I Fix the `indexOf` Method Issue for Arrays in IE8?

IE8's Missing indexOf for Arrays: A Solution

In this common JavaScript function, the use of Array.prototype.indexOf within the condition if ( allowed.indexOf(ext[1]) == -1) causes a problem in IE8. To understand why, let's delve into IE8's unique behavior.

IE8, unlike modern browsers such as Opera, Firefox, and Chrome, lacks an indexOf method for arrays. This omission stems from the fact that the ECMAScript 5 standard, which introduced the indexOf method, was not supported by IE8. As a result, attempts to use the indexOf method on arrays will result in an error in IE8.

To resolve this issue, we can adopt the following strategy:

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 code snippet, sourced from MDN, defines a polyfill for the indexOf method. It ensures that Array.prototype.indexOf is available in all environments, including IE8. By adding this code before using indexOf on arrays, we can ensure that it will function correctly in all browsers, including IE8.

By implementing this solution, the original function will work seamlessly in IE8, allowing developers to check if a specific file extension is allowed in a user-selected file.

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