setTimeout, setInterval, setImmediate, nextTick

const util = require('util');
const process = require('process');
const sleep = util.promisify(setTimeout);

var a = function(callback){
    callback();
}

a(async function(){
    console.log("print me first");
    await sleep(2000);
    console.log("print me in last");
})

//queue callback for execution after given duration
//so the given callback will be executed after all functions and event handlers already queued at that time.
setTimeout( function(){
    console.log("print me after 2000 ms");
},2000)


//after currently executing I/O call back
//similar to setTimeout(callback,0) but it doesn't check queue of functions but only the queue of I/O eventhandlers
//Use setImmediate if you want to queue the function behind whatever I/O event callbacks that are already in the event queue. 
setImmediate( function(){
    console.log("then me on 3rd priority");
})


const timeid= setInterval(function(){ 
    console.log("then me on 2nd priority");
    clearInterval(timeid);
}, 0);

//execute given callback once all the queued functions and event handlers are executed
setTimeout( function(){
    console.log("then me on 2nd priority too");
},0)


//Use process.nextTick to effectively queue the function at the head of the event queue so that it executes immediately after the current function completes.
process.nextTick( function(){//blocking
    console.log("then me on 1st priority");
})




//So in a case where you're trying to break up a long running, CPU-bound job using recursion, you would now want to use setImmediate rather than process.nextTick to queue the next iteration as otherwise any I/O event callbacks wouldn't get the chance to run between iterations.


a(async function(){
    console.log("print me first too");
    await sleep(2000);
    console.log("print me in last too");
})

console.log("print me 2nd");


/* Output
print me first
print me first too
print me 2nd
then me on 1st priority
then me on 2nd priority
then me on 2nd priority too
then me on 3rd priority
print me after 2000 ms
print me in last
print me in last too
*/