19 October 2011

IE7 and "Error: Expected identifier, string or number"

IE7 (and earlier versions) have trouble with errant commas in array declarations. Take this code, provided by James Messinger on Stack Overflow:
<script type="text/javascript">
// Replace the normal jQuery getScript function with one that supports
// debugging and which references the script files as external resources
// rather than inline.
   getScript: function(url, callback) {
      var head = document.getElementsByTagName("head")[0];
      var script = document.createElement("script");
      script.src = url;

      // Handle Script loading
         var done = false;

         // Attach handlers for all browsers
         script.onload = script.onreadystatechange = function(){
            if ( !done && (!this.readyState ||
                  this.readyState == "loaded" || this.readyState == "complete") ) {
               done = true;
               if (callback)

               // Handle memory leak in IE
               script.onload = script.onreadystatechange = null;


      // We handle everything using the script element injection
      return undefined;
   }, // <-- Unneeded comma which blows up IE7.
IE7 blows up with this error:
Error: Expected identifier, string or number
It took quite a bit of debugging and Google searches to finally understand where the problem was. Note the last comma, after the next-to-last closing curly brace "}," -- this is unnecessary. Modern browsers can handle this, but IE7 chokes. Simply remove the comma and you're good to go. More on this problem on Stack Exchange.

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