async keyword doesn't make your function asynchronous

async-is-not-asynchronous.js

function heavyFunc() {
    const limit = Math.pow(10, 8);
    let res = 0;
    for (let i = 1; i < limit; i++) {
        res += Math.atan2(i, i) * Math.random();
    }
    return res;
}

async function heavyFuncWithAsync() {
    const limit = Math.pow(10, 8);
    let res = 0;
    for (let i = 1; i < limit; i++) {
        res += Math.atan2(i, i) * Math.random();
    }
    return res;
}

console.log('Starting heavyFunc. Current timestamp:', performance.now());
const res = heavyFunc();
console.log('Result of heavyFunc:', res);
console.log('Current timestamp:', performance.now());

console.log('Starting heavyFunc with async. Current timestamp:', performance.now());
const asyncRes = heavyFuncWithAsync();
console.log('Result of heavyFunc with async:', asyncRes);
console.log('Current timestamp:', performance.now());

/*
10:36:18.290 async:21 Starting heavyFunc. Current timestamp: 411333.0799999967
10:36:23.573 async:23 Result of heavyFunc: 39269864.55848782
10:36:23.574 async:24 Current timestamp: 416617.12499999703
10:36:23.574 async:26 Starting heavyFunc with async. Current timestamp: 416617.1800000011
10:36:28.570 async:28 Result of heavyFunc with async: Promise {<resolved>: 39267627.19725549}
10:36:28.571 async:29 Current timestamp: 421614.19499999465
*/