You can use many plugins from here already:-
https://www.npmjs.com/
You might need to use a tool call 'Browserify' to convert them to work in the browser/DS if the author has not done so already. Not all plugins will work however (especially if they use file access or low level IO), but any that claim to work in the browser should also work in DS.
A useful trick when using Browerify, is to put something like this into your index.js file (which is required when using Browserify)
window.thePlugin = require( "theplugin.js" )
and then include the Browserified bundle into your app using app.Script(). The 'thePlugin' global variable will then give you access to the object inside the npm package. Alternatively you could add support for the require function into DS, by using one of the available js libs out there.