var xs = xstream.default;

​

var streamA = xs.periodic(100).take(4).map(i => [

  {ts: 1, value: 20}, 

  {ts: 2, value: 10}, 

  {ts: 3, value: 10}, 

  {ts: 4, value: 15}

][i]);

​

var streamB = xs.periodic(120).take(3).map(i => [

  {ts: 1, value: 5}, 

  {ts: 2, value: 20},

  {ts: 4, value: 25}

][i]);

​

var streamOut = xs.combine(

  (a, b) => {

    if (a.ts === b.ts) {

      return {ts: a.ts, value: a.value + b.value};

    } else {

      return null;

    }

  },

  streamA, streamB

).filter(x => x !== null);

​

streamOut.addListener({

  next: i => console.log(i),

  error: err => console.error(err),

  complete: () => console.log('completed'),

})