javascript - Calling function with a Promise hangs when in a loop -


when run following javascript code, works fine. if remove settimeout function call , replace line of code like:

resolve(x);

the browser hang.

the browser appears hang because processing calls processnode function in endless while loop. isn't clear why there blocking going on @ all. processnode returns promise. furthermore, startnodeprocessing async function using await on calls. thought having promise , async function await prevent blocking of thread, i'm wrong. appears settimeout executes code on separate thread preventing blocking. if case, why bother promise or async function start with?

function processnode(x) {     return new promise(resolve => {         console.log("x: " + x + "  " + date.now());         settimeout(() => {             resolve(x);         }, x);     }); }  async function startnodeprocessing() {     while(true) {         var = processnode(1);         var b = processnode(1);         var c = processnode(1);         var d = processnode(1);         var a1 = await a;         var b1 = await b;         var c1 = await c;         var d1 = await d;     }      return; }  startnodeprocessing();

well following happens:

 var = processnode(1); //the parser jumps processnode , creates promise: return new promise(function(resolve) //the promise resolved resolve(x); //the function returns, enter main function again:        var a1 = await a; //await internally calls function: a1.then(return func) //as promise resolved, callback called immeadiately //the parser returns main function

as can see, parser never exits loop, therefore blocking never halts.


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