Higher perf - Map.prototype.forEach or for..of?

Question

Say I have:

const m = new Map();

is there a performance difference between:

for(let v of m){

}

vs.

m.forEach(v => {});

I assume Map.protoype.forEach uses an iterator just like for..of? I read here that's it safe to delete keys from the map during iteration using for..of, see: ES6: Is it dangerous to delete elements from Set/Map during Set/Map iteration?

and I am wondering if it's safe to delete keys from the map with a Map.prototype.forEach loop also.

Answer 1

Did a little benchmark with the following code on node.js 8.11

const Benchmark = require('benchmark');
const suite = new Benchmark.Suite();

suite
  .add('for of', function () {
    const m = new Map();
    for (let i = 0; i < 100; i++) {
      m.set(`key${i}`, i);
    }

    for (let v of m) {
      m.delete(v);
    }
  })
  .add('forEach', function () {
    const m = new Map();
    for (let i = 0; i < 100; i++) {
      m.set(`key${i}`, i);
    }

    m.forEach(v => {
      m.delete(v);
    })
  })
  .on('cycle', function (event) {
    console.log(String(event.target));
  })
  .on('complete', function () {
    console.log('Fastest is ' + this.filter('fastest').map('name'));
  })
  // run async
  .run({ 'async': true });

And the result was pretty interesting:

for of x 88,105 ops/sec ±0.36% (89 runs sampled)
forEach x 81,532 ops/sec ±0.55% (90 runs sampled)
Fastest is for of