Proto-Proimse

chainable_proto_promise.js

function Promise() { };
Promise.prototype = {
  then: function(cb) {
    var p = new Promise();
    this.resolve = function(v) {
      var value = cb(v);
      if (p.resolve) p.resolve(value);
    };
    return p;
  }
}

function somethingAsync() {
  var p = new Promise();
  setTimeout(function () { p.resolve(42); }, 1000);
  return p;
}

somethingAsync()
  .then(function (v) { console.log(v); return v * 2 })
  .then(function (v2) { console.log(v2); return v2 * 3 })
  .then(function (v3) { console.log(v3); });

proto_promise.js

// simulate async data retrieval
function retrieveTemperatureFromRemote(cb) {
	setTimeout(function() { cb(42) }, 1000)
}

class Promise2 {

  resolve(v) { console.log("resolve", this); this.result = v }
  then(cb) {
    console.log("then", this)
    if (this.result !== undefined)
      cb(this.result)
    else
      this.resolve = cb
  }
}

function promiseRetrieveTemperatureFromRemote() {
  var promise = new Promise2()
  retrieveTemperatureFromRemote(v => promise.resolve(v))
  return promise
}

var p = promiseRetrieveTemperatureFromRemote()

proto_promise_without_promise.js

// simulate async data retrieval
function retrieveTemperatureFromRemote(cb) {
	setTimeout(function() { cb(42) }, 1000)
}

function promiseRetrieveTemperatureFromRemote() {
  var result = undefined
  var resolve = v => result = v
  var then = (cb) => {
    if (result !== undefined)
      cb(result)
    else
      resolve = cb
  }

  retrieveTemperatureFromRemote(v => resolve(v) )
  return {
    then: then
  }
}

var p = promiseRetrieveTemperatureFromRemote()
p.then(v => console.log(v))