Sample from the second stream every time an event occurs on the first stream.
Graph
a: {--t--t--t-------t}
b: {---1---2---3---4-}
sampleOn(a, b): {-----1--2-------4}
Signature
Stream a -> Stream b -> Stream b
Usage
const sampleOn = require('flyd/module/sampleon')
const sample = flyd.stream()
const on = flyd.stream()
const result = sampleOn(on, sample)
on(true)
result() // undefined
sample(1)
on(true)
result() // 1
sample(2)
sample(3)
on(true)
result() // 3