Latency Performance calculations for React-Worker-DOM

React-Worker-Latency.js

var start, results = [];
var ITERATIONS = 100;
var addButton = document.querySelectorAll('.btn.btn-primary')[0];
var addItem = function() {
    if (results.length < ITERATIONS) {
        start = performance.now();
        addButton.click();
    } else {
        console.log('Testing done, average is %s milliseconds, all data is', results.reduce(function(a, b) {
            return a + b;
        }, 0) / results.length);
    }
}

addItem(); // set the first item
window.setTimeout(function() {
    var list = document.getElementsByTagName('ol')[0];
    new MutationObserver(function(mutations) {
        results.push(performance.now() - start);
        window.setTimeout(addItem, 100);
    }).observe(list, {
        childList: true
    });
    addItem();
}, 1000);