JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#" onclick="doit()">Test Array Perf</a>

JavaScript

requestIdleCallback(async function () {
    function waitForIdle(){return new Promise(requestIdleCAllback)}
    var size = 1000 * 1000;
    var reps = 100;

    console.log(reps + " reps of size " + size+" on "+navigator.userAgent);

    console.time("StaticArray");
    var buffer = new ArrayBuffer(size);
    var int8View = new Int8Array(buffer);
    for (j = 0; j < reps; j++) {
        for (i = 0; i < size; i++) {
            int8View[i] = 4; // http://xkcd.com/221/ 
        }
    }
    console.timeEnd("StaticArray");


    console.time("Int32Array");
    var buffer2 = new ArrayBuffer(size * 4);
    var int32View = new Int32Array(buffer2);
    for (j = 0; j < reps; j++) {
        for (i = 0; i < size; i++) {
            int32View[i] = 4; // http://xkcd.com/221/ 
        }
    }
    console.timeEnd("Int32Array");

    console.time("Array");
    var arr = [];

    for (j = 0; j < reps; j++) {
        for (i = 0; i < size; i++) {
            arr[i] = 4;
        }
    }

    console.timeEnd("Array");
});