For loop with `var` vs `let`

README.md

For loop with var vs let

Using a var instead of a let in a for loop was a game changer with Node.js 6 but now it's merely the same performances.

for (var i = 0; i < 10000; i++) {
  // ...
}

for (let i = 0; i < 10000; i++) {
  // ...
}

Results

Node 6

for var x 156,390 ops/sec ±1.12% (83 runs sampled)
for let x 99,355 ops/sec ±0.80% (89 runs sampled)
Fastest is for var

Node 8

for var x 126,389 ops/sec ±1.26% (86 runs sampled)
for let x 131,086 ops/sec ±1.27% (91 runs sampled)
Fastest is for let

Node 10

for let x 141,522 ops/sec ±0.93% (89 runs sampled)
for var x 141,682 ops/sec ±0.75% (93 runs sampled)
Fastest is for var,for let

Node 12

for let x 142,272 ops/sec ±0.85% (87 runs sampled)
for var x 149,323 ops/sec ±0.48% (93 runs sampled)
Fastest is for var

Node 14

for let x 143,337 ops/sec ±0.86% (90 runs sampled)
for var x 150,583 ops/sec ±0.69% (94 runs sampled)
Fastest is for var

Node 16

for let x 153,116 ops/sec ±0.87% (88 runs sampled)
for var x 157,170 ops/sec ±0.53% (94 runs sampled)
Fastest is for var

bench.js

const { Benchmark } = require("benchmark");
var suite = new Benchmark.Suite();

const array = [];
for (var i = 0; i < 1000; i++) {
  array.push(i);
}
let ret;

// add tests
suite
  .add("for var", function () {
    ret = [];

    for (var i = 0; i < array.length; i++) {
      ret.push(i);
    }
  })
  .add("for let", function () {
    ret = [];

    for (let i = 0; i < array.length; i++) {
      ret.push(i);
    }
  })
  // add listeners
  .on("cycle", function (event) {
    console.log(String(event.target));
  })
  .on("complete", function () {
    console.log("Fastest is " + this.filter("fastest").map("name"));
  })
  // run async
  .run();

So it's this (small) cost that we can see in this benchmark right?

Also, using var could result in a higher memory usage ?