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



}