javascript - how to defer resolve tasks in nodejs -

i new nodejs, not sure how arrange tasks in order such behave correctly.

below 2 examples

arr.foreach(function(elem){     //do many many things }); console.log('done, take ur pick'); stdin.on('input', function action(){     ... }) 

how can set stdin.on fire after arr.foreach. , question 2 think if do

fn1(); fn2();  function fn1(){     //long long code }  function fn2(){     console.log('fn2 done!') } 

and runs above, execution in thread of

fn1 fn2 fn1 fn1 fn1, right? how prevent this?

functions in node.js either synchronous or asynchronous. synchronous code runs in single thread, , behaves code you're used to:

fn1(); fn2(); fn3(fn4()); 

will run fn1, fn2, fn4, fn3 (passing in result of fn4 parameter).

asynchronous code fires off action, , takes parameter function execute when it's done (which might, in turn, fire off asynchronous action). control immediately. example:

dosomeasyncthing(function () {     console.log("did async thing"); }); console.log("hello"); 

executes this: first, asynchronous action fired off, "hello" printed. time later, asynchronous action completes, callback called, , "did async thing" printed.

if want 1 asynchronous thing, asynchronous thing after first 1 finished, standard way nest callbacks:

async1(function() {     async2(function() {         console.log("async1 , async2 finished");     }); }); 

although there better options.

so in second example, if fn1 synchronous, work wrote it. if fn1 has asynchronous, have asynchronous, have write this:

function fn1(callback) {     // sync stuff     dosomethingasync(function () {         // more sync stuff         dosomethingmoreasync(function () {             // more sync stuff             callback(); // call callback once completed         });     }); } 

and call this

fn1(function () {     fn2(); }); 

which simplified to:

fn1(fn2); 

in first example, note array.foreach synchronous. if // many many things synchronous, work wrote it, if there's asynchronous action in there, can either manually implement counter, or use async library or promise iterator utilities.