Answer by rmirabelle for How can I check if a jQuery plugin is loaded?

If we're talking about a proper jQuery plugin (one that extends the fn namespace), then the proper way to detect the plugin would be:

if(typeof $.fn.pluginname !== 'undefined') { ... }

Or because every plugin is pretty much guaranteed to have some value that equates to true, you can use the shorter

if ($.fn.pluginname) { ... }

BTW, the $ and jQuery are interchangable, as the odd-looking wrapper around a plugin demonstrates:

(function($) {    //})(jQuery))

the closure

(function($) {    //})

is followed immediately by a call to that closure 'passing' jQuery as the parameter

(jQuery)

the $ in the closure is set equal to jQuery