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

Generally speaking, jQuery plugins are namespaces on the jQuery scope. You could run a simple check to see if the namespace exists:

 if(jQuery().pluginName) {     //run plugin dependent code }

dateJs however is not a jQuery plugin. It modifies/extends the javascript date object, and is not added as a jQuery namespace. You could check if the method you need exists, for example:

 if(Date.today) {      //Use the dateJS today() method }

But you might run into problems where the API overlaps the native Date API.