Sequences n-simulteniously promises.js

function MakeQuerablePromise(promise) {
      // Don't create a wrapper for promises that can already be queried.
      if (promise.isResolved) return promise;

      var isResolved = false;
      var isRejected = false;

      // Observe the promise, saving the fulfillment in a closure scope.
      var result = promise.then(
         function(v) { isResolved = true; return v; },
         function(e) { isRejected = true; throw e; });
      result.isFulfilled = function() { return isResolved || isRejected; };
      result.isResolved = function() { return isResolved; }
      result.isRejected = function() { return isRejected; }
      return result;
  }

    var functions = [
      function() {
        console.log('start 1');
        return new Promise((res, rej) => { setTimeout((undefined) => { console.log('finish 1'); res() }, 1000, 1) });
      },

    	function(){
        console.log('start 2');
      	return new Promise((res, rej) => { setTimeout((undefined) => { console.log('finish 2'); res() }, 2000, 2) });
    	},
    	function(){
        	console.log('start 3');
      	return new Promise((res, rej) => { setTimeout((undefined) => { console.log('finish 3'); res() }, 3000, 3) });
    	},
    	function(){
  	    console.log('start 4');
      	return new Promise((res, rej) => { setTimeout((undefined) => { console.log('finish 4'); res() }, 4000, 4) });
    	},
    	function(){
  	    console.log('start 5');
      	return new Promise((res, rej) => { setTimeout((undefined) => { console.log('finish 5'); res() }, 5000, 5) });
    	},
    	function(){
        	console.log('start 6');
      	return new Promise((res, rej) => { setTimeout((undefined) => { console.log('finish 6'); res() }, 6000, 6) });
    	},
    ];

    var startStack = functions.splice(0,2).map((fn) => MakeQuerablePromise(fn()) );

    functions.reduce(function(promise, fn) {
      return promise.then(function() {
        startStack = startStack.filter((i) => !i.isFulfilled())
        startStack.push(MakeQuerablePromise(fn()));
        return Promise.race(startStack);
      });
    }, Promise.race(startStack));