bencode with Buffer()s from nodejs (as it is binary data, javascript string are not a good idea to handle it)
npm install dht-bencode
var bencode = require('dht-bencode');
bencode.bencode({ t: 'ab' }).toString(); // should result in "d1:t2:abe"
bencode.bdecode("d1:t2:abe"); // should result in { t: <Buffer 61 62> }