Check event loop health by checking it's delay

event-loop-delay-check.js

const interval = 1000;
const acceptableDelay = 3;
let lastCheck = 0;

(function checkEventLoop() {
    const now = Date.now();
    if (lastCheck)
        if (now - lastCheck > interval + acceptableDelay) {
            console.log('\x1b[31m', 'event loop delay', (now - lastCheck - interval) + 'ms', '\x1b[0m');
        } else
            console.log('\x1b[32m', 'event loop delay', (now - lastCheck - interval) + 'ms', '\x1b[0m');


    lastCheck = Date.now();
    setTimeout(() => {
        checkEventLoop();
    }, interval);
})();

(function initHeavyTask() {
    const heavyTask = () => {
        console.log('heavyTask start');
        for (let i = 0; i < 1e8; i++) {
            (Math.sqrt(Math.random() * 1000));
        }
        console.log('heavyTask end');
        setTimeout(() => {
            heavyTask();
        }, Math.random() * 10000);
    }
    setTimeout(() => {
        heavyTask();
    }, 3000);
})();