Plus+ Members on OpenProcessing can add custom javascript libraries to their sketches. 

To add an external library hosted on a domain,  click on "+ Add custom library" below the libraries section on the code options panel, and copy/paste the URL of the javascript library you would like to add.
Make sure you use an "https" secure address, otherwise browser will not load your library.
You can also upload a javascript file on the files panel, and add its filename here to add it locally. Eg. myLibrary.js

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