This is a very short post on some useful tidbits I’ve learnt using the ubiquitous jQuery library. I have occasionally found myself in a sticky situation because either (a) the library had not loaded, (b) I’ve been using the wrong version.

We can check if the library is available to us by using either a bang (or two), or using the instanceofoperator. We can use jQuery and $ interchangeably, as they are aliases.

// Load library if it hasn't already
if (!window.jQuery) { 
  // code goes here ...

if (typeof window.jQuery == 'undefined') {
  // 'ere be code ... 

In the previous example we used window.jQuery as this will simply result in a truthy output. Using just jQuery or $ alone with the leading bang will lead to a reference error.

We can get the version number by logging one of the following,

// Either ...
jQuery.fn.jquery // or jQuery().jquery

// or equivalently
$.fn.jquery // or $().jquery

Of course, we would need to know the library had already loaded before checking the version!

Short and sweet!

All the best,


Tom Martin

Developer, London, UK