Benchmark cycles (var)

benchmark-cycles-var.js

/******************************************************************************/
'use strict';
/******************************************************************************/
// via https://twitter.com/bmeurer/status/821804688454680576

console.log(`
  // v8 ${process.versions.v8} (Node.js ${process.versions.node})
`);

function f1(a) {
  var x = 0;
  for (var i = 0, l = a.length; i < l; ++i) x += a[i];
  return x;
}

function f2(a) {
  var x = 0;
  for (var y of a) x += y;
  return x;
}

function f3(a) {
  var x = 0;
  a.forEach((y) => { x += y; });
  return x;
}

const a = [];
for (let i = 0; i < 1000; ++i) a[i] = i;

function bench(f) {
  for (let i = 0; i < 1000; ++i) f.call(null, a);
}

for (let i = 0; i < 10; ++i) {
  bench(f1);
  bench(f2);
  bench(f3);
}

console.time('for    ');
bench(f1);
console.timeEnd('for    ');

console.time('for-of ');
bench(f2);
console.timeEnd('for-of ');

console.time('forEach');
bench(f3);
console.timeEnd('forEach');

See this more resumptive benchmark with some results in the comments for several v8 / Node.js versions.