How can I check if a jQuery plugin is loaded?

Question

Is there any way to check if a particular plugin is available?

Imagine that you are developing a plugin that depends on another plugin being loaded.

For example I want the jQuery Validation plugin to use the dateJS library to check if a given date is valid. What would be the best way to detect, in the jQuery Valdation plugin if the dateJS was available?

Answer 1

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.