ES6 Iterator Timing

esIterTest.js

function foo() {
  'use strict';
  
class MyArrayIterator {

  constructor(source) {
    this._index = 0;
    this._source = source;
  }

  next() {
    if (this._index >= this._source.length) {
      return undefined;
    }
    return this._source[this._index++];
  }
}

class ESArrayIterator {

  constructor(source) {
    this._index = 0;
    this._source = source;
  }

  [Symbol.iterator]() {
    return this;
  }

  next() {
    if (this._index >= this._source.length) {
      return { done: true };
    }
    return { done: false, value: this._source[this._index++] };
  }
}

function mySum(it) {
  let v;
  let r = 0;
  while ((v = it.next()) !== undefined) {
    r += v;
  }
  return r;
}

function esSum(it) {
  let r = 0;
  for (let v of it) {
    r += v;
  }
  return r;
}

function esSum2(it) {
  let r = 0;
  while (true) {
    let { done, value } = it.next();
    if (done) {
      return r;
    }
    r += value;
  }
}
  
function makeData() {
  let data = [];
  for (let i = 0; i < 1000000; ++i) {
    data.push(Math.random());
  }
  return data;
}

var data = makeData();

function myTiming() {
  let it = new MyArrayIterator(data);
  let t1 = performance.now();
  let r = mySum(it);
  let t2 = performance.now();
  return [r, t2 - t1];
}

function esTiming() {
  let it = new ESArrayIterator(data);
  let t1 = performance.now();
  let r = esSum(it);
  let t2 = performance.now();
  return [r, t2 - t1];
}

function esTiming2() {
  let it = new ESArrayIterator(data);
  let t1 = performance.now();
  let r = esSum2(it);
  let t2 = performance.now();
  return [r, t2 - t1];
}
 return {myTiming, esTiming, esTiming2}; 
}

let things = foo();
myTiming = things.myTiming;
esTiming = things.esTiming;
esTiming2 = things.esTiming2;