JSFiddle - React, Tailwind, and code Playground

JavaScript

let a = Array.from({length: 1e6}, () => Math.random());

let _fun = (d) => d.map(v => v * 2);

let _for = (d, typed) => {
	let b = typed ? new Float32Array(d.length) : Array(d.length);
  
  for (let i = 0; i < d.length; i++) {
		b[i] = d[i] * 2;
  }
  
  return b;
};

// fun
console.time('_fun');
_fun(a);
console.timeEnd('_fun');
console.time('_fun');
_fun(a);
console.timeEnd('_fun');
console.time('_fun');
_fun(a);
console.timeEnd('_fun');
console.time('_fun');
_fun(a);
console.timeEnd('_fun');

// for
console.time('_for');
_for(a);
console.timeEnd('_for');
console.time('_for');
_for(a);
console.timeEnd('_for');
console.time('_for');
_for(a);
console.timeEnd('_for');
console.time('_for');
_for(a);
console.timeEnd('_for');

// for typed
console.time('_for/typed');
_for(a, true);
console.timeEnd('_for/typed');
console.time('_for/typed');
_for(a, true);
console.timeEnd('_for/typed');
console.time('_for/typed');
_for(a, true);
console.timeEnd('_for/typed');
console.time('_for/typed');
_for(a, true);
console.timeEnd('_for/typed');