Javascript Library
The Javascript Library is the most established and used one there is. It has all the necessary functionality to fully use IOTA, including wrapper API functions, cryptography-related functions and the core API. The Javascript library can be easily used in the browser, either by directly requiring it in your code, or via bower; or via npm locally.
npm install iota.lib.js
bower install iota.lib.js
The full documentation can be seen here: https://github.com/iotaledger/iota.lib.js.
If you want to get more examples of how to use the library, head over to https://learn.iota.org