How does async work in NodeJS

async.js

async function callme(message, level) {
    console.log(message, "entering", level)
    level--;

    // let req = new XMLHttpRequest();
    // req.open('GET', "https://thumbs.dreamstime.com/b/brown-dog-corso-corso-stands-field-green-grass-brown-dog-corso-cors-120197441.jpg");
    // req.onload = function () {
    //     if (req.status == 200) {
    //         console.log(req.status, "Download ok");
    //     } else {
    //         console.log("File not Found");
    //     }
    // };
    // req.send();

    for (let i = 0; i < 100; i++) {
        console.log(message, "Looping to " + i + " at level: " + level)
        // if (level > 0) {
        //     callme("in forloop", -1);
        //     console.log("###")
        // }
    }
}

const started = Date.now();
console.log("Started: " + started);

setTimeout(function(){ 
    const inCallback = Date.now();
    console.log("In setTimeout callback: " + inCallback, inCallback - started);    
    console.log("Called after " + "10 milsec");
 }, 0);

callme("Not important", -1);
callme("In main", -1).then(() => new Promise((res) => {
    return res(1)
})).then((val) => {
    console.log('log', val);
});

console.log("Should print");