Capture Javascript error for Selenium WebDriver

JSError.js

//Client side utilities for Selenium tests of ExtJS web applications
//requires ExtJS and Underscore libraries
//SJTXE - Selenium JavaScript Testing eXtension for ExtJS
(function(root, Ext) {
    var root = root || window;
    var me = root;
    var Ext = Ext;
    //private vars
    var hasJSError = false;
      
    var onJSError = function(conn, response, options, eOpts) {        
        hasJSFailure = true;
    };
    
    window.onerror = onJSError;
         
    //exposed object
    var SJTXE = {
        VERSION: '0.0',
        hasJSError: function() {return hasJSError}
    };
    root.SJTXE = SJTXE;
    
    return SJTXE;
})(this, Ext);