Test execution time of Array.fill() vs Array.push()

array-fill-with-generator-and-sorting.js

function generator() {
  let id = 0;
  return () => id++;
}

function arrayFill(times, generator, sortFn = () => 0) {
  return Array(times)
    .fill(null)
    .map(generator)
    .sort(sortFn);
}

function arrayOf(times, generator, sortFn = null) {
  const result = [];

  for (let i = 0; i < times; ++i) {
    result.push(generator());
  }

  return sortFn
    ? result.sort(sortFn)
    : result;
}

function test(items, testFunction, sortFn, type) {
  const start = Date.now();
  const result = testFunction(items, generator(), sortFn);
  const end = Date.now();

  console.log(type, `${(end - start)/1000}s`, result.length);
}

const totalItems = 10000000;

test(totalItems, arrayFill, undefined, 'arrayFill');
test(totalItems, arrayOf, undefined, 'arrayOf');

const sortFn = (a, b) => a > b ? 1  : -1;
test(totalItems, arrayFill, sortFn, 'arrayFill with sort');
test(totalItems, arrayOf, sortFn, 'arrayOf with sort');


// Result
// arrayFill 2.743s
// arrayOf 0.349s
// arrayFill with sort 8.824s
// arrayOf with sort 6.461s