streams everywhere!

streams.js

const Rx = require('rxjs/Rx')

const getB = (a, cb) => setTimeout(a => cb(null, a+'b'), 10000)
const getbAsObservable = Rx.Observable.bindNodeCallback(getB)

const a$ = Rx.Observable.from([1, 2, 3])
const b$ = a$.map(a => getbAsObservable(a))
const c$ = a$.zip(b$.mergeAll())

c$.subscribe(data => console.log(data))

current output:

[ 1, 'undefinedb' ]
[ 2, 'undefinedb' ]
[ 3, 'undefinedb' ]

desired output:

[ 1, '1b' ]
[ 2, '2b' ]
[ 3, '3b' ]