parallel / series requests with js-csp

csp.js

var csp = require('js-csp'),
  { chan, putAsync, take, go, put, timeout, spawn} = csp,
  request = require('superagent');

var urls = ['http://www.google.com', 'http://www.jlongster.com', 'http://www.myntra.com'];

go(function*(){  
  // 1. do a bunch of requests in parallel, and save their response lengths
  var parallel = yield map(urls, function*(url){
    return (yield fetch(url)).text.length;
  });
  console.log(parallel);  //  [ 19643, 12148, 285823 ]
  // neat!

  // 2. the same, but in series
  var queue = yield mapSeries(urls, function*(url){
    return (yield fetch(url)).text.length;
  });
  console.log(queue);     //  [ 19683, 12148, 285826 ]
});


// make a request, put its response on a channel
function fetch(url){
  var c = chan();
  request.get(url).end((err, res)=> {putAsync(c, err || res);  c.close();});
  return c;
}

function map(arr, gen){
  return go(function*(){
    var chs = arr.map(val => spawn(gen(val)));
    var ret = [];
    for(var i=0;i<chs.length;i++){
      ret.push(yield chs[i])
    }
    return yield ret;
  })
}

function mapSeries(arr, gen){
  return go(function*(){
    var ret = [];
    for(var i=0;i<arr.length;i++){
      ret.push(yield spawn(gen(arr[i])))
    }
    return yield ret;
  })
}