Monday, February 13, 2012

Is it possible to lazy load Jquery (not a plugin)?

I've got several JavaScript files that load along with many of my pages, costing valuable tens of kilobytes of data download. One of these is a version of jquery.min.js which although minified, is still 25kb or so.

My issue is that a huge chunk of mobile phones don't support JavaScript so the downloading of this and other JS files is a waste of data. Is there anyway to lazy load the JQuery file by adding a <script> tag in the page that calls the JS file and would obviously only execute if a browser supports JavaScript, which would only then make sense to download it?


  1. To load script files only under certain conditions, I have used something like:

    <script type="text/javascript">
    document.write('<scr'+'ipt type="text/javascript" src="/js/jquery.min.js"></scr'+'ipt>');

    Note: this only works inline, after the document is done loading, document.write() will have undesired effects.

    Note 2: It is important to break '</script>' like '</scr'+'ipt>' so as to not confuse the browser's parser into thinking your true script block is ended. I do the opening script tag the same way for good measure.

  2. function loadScript(filename) {
    var t = document.createElement('script'),
    s = document.getElementsByTagName('body')[0];

    t.type = 'text/javascript';
    t.async = true;
    t.src = filename;

    // If and when jQuery is needed, you'd load it with: