Javascript executes twice in Internet Explorer

I currently ran into a problem where a lazy loaded javascript would execute twice using internet explorer - and ONLY internet explorer (currently version 9). Firefox and chrome works. Here is my code:

injectExternalJavaScript: function(fileUrl) {
    return jQuery.Deferred(function(deferred) {
        var script = document.createElement('script');
        script['src'] = fileUrl;
        script['type'] = 'text/javascript';
        var head = document.getElementsByTagName("head")[0];
        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;
                script['onload'] = script['onreadystatechange'] = null;
                head.removeChild(script);
                deferred.resolve();
            }
        };
        head.appendChild(script);
    }).promise();
}

I already found this posting and changed my code according to it but still ie is executing my script twice. You guys got any ideas?

Edit: This is my solution

injectExternalJavaScript: function(fileUrl) {
    return jQuery.Deferred(function(deferred) {
        var script = document.createElement('script');
        script['src'] = fileUrl;
        script['type'] = 'text/javascript';
        var head = document.getElementsByTagName("head")[0];
        var done = false;
        // Attach handlers for all browsers
        var cb = function() {
            if (!done && (!this.readyState || this.readyState === "loaded" || this.readyState === 'complete')) {
                done = true;
                script['onload'] = script['onreadystatechange'] = null;
                head.removeChild(scr