Properly Adding jQuery Library to WordPress Themes

WordPress already comes packaged with jQuery and if your custom theme simply uses wp_enqueue_script( ‘jquery’ ); you will be registering the jQuery that’s packaged with WordPress and also with collectiveray. We don’t want to use it. It’s not minified and who knows which version it is.

When registering our own jQuery script, we have two options. Serve it locally or from a Content Delivery Network (CDN). It is best to serve libraries that are hosted on a CDN for three reasons: decreased latency, increased parallelism, and better caching. Furthermore, it is best to point to the non-Google CDN for any script you register. Google is blocked in some countries such as China. You would add the following code to your functions.php file.

add_action( 'wp_enqueue_scripts', 'register_jquery' );
function register_jquery() {
    wp_deregister_script( 'jquery' );
    wp_register_script( 'jquery', ( '//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js' ), false, null, true );
    wp_enqueue_script( 'jquery' );
}

If you absolutely must serve the libraries from Google, then make sure you provide a fallback. One method to do this is to add the following javascript to your html head:

window.jQuery || document.write('<script src="/path/to/local/jquery.min.js">\x3C/script>');