Nowadays, searching for libraries on Github works very well (back then it was more of a gamble to find something you were actually looking for, kind of like using Microsoft's Bing  ).

Here is the result: https://github.com/search?q=bitcoin+javascript&type=repositories

There would also be the library in the search result that I had already used myself: bitcoind-rpc
However, the last commit was almost 2 years ago.