Array performance quiz

array-perf.js

// Which iteration in the fastest?

// each number is in range [0 .. 255]

import { bench, run } from 'mitata';

var arr1 = [];  // array of { rand: number } objects
var arr2 = [];  // array of numbers
var arr3 = [];  // array of numbers, iterated with forEach
var arr4 = [];  // array of numbers packed into 4-byte integers
var arr5;       // Uint8Array
var arr6 = [];  // array of numbers, iterated with for .. of

var MAX_LEN = 20000000;

for (var i = 0; i < MAX_LEN; i++) {
    var rand = Math.floor(Math.random() * 256);

    arr1.push({ rand });
    arr2.push(rand);
    arr3.push(rand);
    arr6.push(rand);

    if (i % 4 === 3) {
        arr4.push(arr2[i-3] << 24 | arr2[i-2] << 16 | arr2[i-1] << 8 | arr2[i]);
    }
}
arr5 = new Uint8Array(arr2);

var sum, len;

// Benchmark starts here

bench('1. array of { rand: number } objects', () => {
    sum = 0;

    for (var i = 0; i < MAX_LEN; i++) {
        sum += arr1[i].rand;
    }
});

bench('2. array of numbers', () => {
    sum = 0;

    for (var i = 0; i < MAX_LEN; i++) {
        sum += arr2[i];
    }
});

bench('3. array of numbers, iterated with forEach', () => {
    sum = 0;

    arr2.forEach(function (val) {
        sum += val;
    });
});

bench('4. array of numbers packed into 4-byte integers', () => {
    sum = 0;
    len = arr4.length;

    for (var i = 0; i < MAX_LEN; i++) {
        if (i >= len) continue; // keeping the same amount of iterations, just for fun

        sum += (arr4[i] >>> 24) + ((arr4[i] >>> 16) & 0xff) + ((arr4[i] >>> 8) & 0xff) + (arr4[i] & 0xff);
    }
});

bench('5. Uint8Array', () => {
    sum = 0;
    len = arr5.length;

    for (var i = 0; i < len; i++) {
        sum += arr5[i];
    }
});

bench('6. array of numbers, iterated with for .. of', () => {
    sum = 0;
    len = arr6.length;

    for (var val of arr6) {
        sum += val;
    }
});

await run({});