Related
I am making a chrome extension (mv3). Based on user activity, the content.js passes a message to the background.js which then calls an async function to add data in Google Docs using Docs API.
I want each request to execute only after the previous one has finished running. I am using chrome.runtime.sendMessage to send a message from content.js and don't see a way of calling background.js serially from there. So I need a way of executing them one by one in background.js only. The order of these requests is also important (but if the order of the requests gets changed by one/two places, I think that would still be okay from a user perspective).
I tried something and it is working but I am not sure if I am missing some edge cases, because I was unable to find the approach in any other answers -
Semaphore-like queue in javascript?
Run n number of async function before calling another method in nodejs
JavaScript: execute async function one by one
The approach I used is: I use a stack like structure to store requests, use setInterval to check for any pending requests and execute them serially.
content.js:
chrome.runtime.sendMessage({message});
background.js:
let addToDocInterval = "";
let addToDocCalls = [];
async function addToDoc(msg) {
// Await calls to doc API
}
async function addToDocHelper() {
if(addToDocCalls.length === 0)
return;
clearInterval(addToDocInterval)
while(addToDocCalls.length > 0) {
let msg = addToDocCalls.shift();
await addToDoc(msg);
}
addToDocInterval = setInterval(addToDocHelper, 1000);
}
chrome.runtime.onMessage.addListener((msg) => {
// Some other logic
addToDocCalls.push(msg);
})
addToDocInterval = setInterval(addToDocHelper, 1000);
Is this approach correct? Or is there any better way to do this?
I'd suggest changing several things.
Don't use timers polling the array. Just initiate processing the array anytime you add a new item to the array.
Keep a flag on whether if you're already processing the array so you don't start duplicate processing.
Use a class to encapsulate this functionality into an object.
Encapsulate the addToDocCalls array and adding to it so your class is managing it and outside code just calls a function to add to it which also triggers the processing. Basically, you're making it so callers don't have to know how the insides work. They just call helper.addMsg(msg) and the class instance does all the work.
Here's an implementation:
async function addToDoc(msg) {
// Await calls to doc API
}
class docHelper {
constructor() {
this.addToDocCalls = [];
this.loopRunning = false;
}
addMsg(msg) {
// add item to the queue and initiate processing of the queue
this.addToDocCalls.push(msg);
this.process();
}
async process() {
// don't run this loop twice if we're already running it
if (this.loopRunning) return;
try {
this.loopRunning = true;
// process all items in the addToDocCalls we have
while(this.addToDocCalls.length > 0) {
let msg = addToDocCalls.shift();
await addToDoc(msg);
}
} finally {
this.loopRunning = false;
}
}
}
const helper = new docHelper();
chrome.runtime.onMessage.addListener((msg) => {
// Some other logic
helper.addMsg(msg);
});
So, process() will run until the array is empty. Any interim calls to addMsg while process() is running will add more items to array and will call process() again, but the loopRunning flag will keep it from starting duplicate processing loops. If addMsg() is called while process is not running, it will start the process loop.
P.S. You also need to figure out what sort of error handling you want if addToDoc(msg) rejects. This code protects the this.loopRunning flag if it rejects, but doesn't actually handle a reject error. In code like this that is processing a queue, often times all you can really do is log the error and move on, but you need to decide what is the proper course of action on a rejection.
You don't need to use setTimeout. You do not even need a while loop.
let addToDocInterval = "";
let addToDocCalls = [];
let running = false;
async function addToDoc(msg) {
// Await calls to doc API
}
async function addToDocHelper() {
if(running || addToDocCalls.length === 0)
return;
running = true;
let msg = addToDocCalls.shift();
await addToDoc(msg);
running = false;
addToDocHelper();
}
chrome.runtime.onMessage.addListener((msg) => {
// Some other logic
addToDocCalls.push(msg);
addToDocHelper();
});
The code should be self explanatory. There is no magic.
Here is a generic way to run async tasks sequentially (and add more tasks to the queue at any time).
const tasks = [];
let taskInProgress = false;
async function qTask(newTask) {
if (newTask) tasks.push(newTask);
if (tasks.length === 0) return;
if (taskInProgress) return;
const nextTask = tasks.shift();
taskInProgress = true;
try {
await nextTask();
} finally {
taskInProgress = false;
//use setTimeout so call stack can't overflow
setTimeout(qTask, 0);
}
}
//the code below is just used to demonstrate the code above works
async function test() {
console.log(`queuing first task`);
qTask(async () => {
await delay(500); //pretend this task takes 0.5 seconds
console.log('first task started');
throw 'demonstrate error does not ruin task queue';
console.log('first task finished');
});
for (let i = 0; i < 5; i++) {
console.log(`queuing task ${i}`)
qTask(async () => {
await delay(200); //pretend this task takes 0.2 seconds
console.log(`task ${i} ran`);
});
}
await delay(1000); //wait 1 second
console.log(`queuing extra task`);
qTask(async () => {
console.log('extra task ran');
});
await delay(3000); //wait 3 seconds
console.log(`queuing last task`);
qTask(async () => {
console.log('last task ran');
});
}
test();
function delay(ms) {
return new Promise(resolve => {
setTimeout(resolve, ms);
});
}
How can I make a simple, non-block Javascript function call? For example:
//begin the program
console.log('begin');
nonBlockingIncrement(10000000);
console.log('do more stuff');
//define the slow function; this would normally be a server call
function nonBlockingIncrement(n){
var i=0;
while(i<n){
i++;
}
console.log('0 incremented to '+i);
}
outputs
"beginPage"
"0 incremented to 10000000"
"do more stuff"
How can I form this simple loop to execute asynchronously and output the results via a callback function? The idea is to not block "do more stuff":
"beginPage"
"do more stuff"
"0 incremented to 10000000"
I've tried following tutorials on callbacks and continuations, but they all seem to rely on external libraries or functions. None of them answer the question in a vacuum: how does one write Javascript code to be non-blocking!?
I have searched very hard for this answer before asking; please don't assume I didn't look. Everything I found is Node.js specific ([1], [2], [3], [4], [5]) or otherwise specific to other functions or libraries ([6], [7], [8], [9], [10], [11]), notably JQuery and setTimeout(). Please help me write non-blocking code using Javascript, not Javascript-written tools like JQuery and Node. Kindly reread the question before marking it as duplicate.
To make your loop non-blocking, you must break it into sections and allow the JS event processing loop to consume user events before carrying on to the next section.
The easiest way to achieve this is to do a certain amount of work, and then use setTimeout(..., 0) to queue the next chunk of work. Crucially, that queueing allows the JS event loop to process any events that have been queued in the meantime before going on to the next piece of work:
function yieldingLoop(count, chunksize, callback, finished) {
var i = 0;
(function chunk() {
var end = Math.min(i + chunksize, count);
for ( ; i < end; ++i) {
callback.call(null, i);
}
if (i < count) {
setTimeout(chunk, 0);
} else {
finished.call(null);
}
})();
}
with usage:
yieldingLoop(1000000, 1000, function(i) {
// use i here
}, function() {
// loop done here
});
See http://jsfiddle.net/alnitak/x3bwjjo6/ for a demo where the callback function just sets a variable to the current iteration count, and a separate setTimeout based loop polls the current value of that variable and updates the page with its value.
SetTimeout with callbacks is the way to go. Though, understand your function scopes are not the same as in C# or another multi-threaded environment.
Javascript does not wait for your function's callback to finish.
If you say:
function doThisThing(theseArgs) {
setTimeout(function (theseArgs) { doThatOtherThing(theseArgs); }, 1000);
alert('hello world');
}
Your alert will fire before the function you passed will.
The difference being that alert blocked the thread, but your callback did not.
There are in general two ways to do this as far as I know. One is to use setTimeout (or requestAnimationFrame if you are doing this in a supporting environment). #Alnitak shown how to do this in another answer. Another way is to use a web worker to finish your blocking logic in a separate thread, so that the main UI thread is not blocked.
Using requestAnimationFrame or setTimeout:
//begin the program
console.log('begin');
nonBlockingIncrement(100, function (currentI, done) {
if (done) {
console.log('0 incremented to ' + currentI);
}
});
console.log('do more stuff');
//define the slow function; this would normally be a server call
function nonBlockingIncrement(n, callback){
var i = 0;
function loop () {
if (i < n) {
i++;
callback(i, false);
(window.requestAnimationFrame || window.setTimeout)(loop);
}
else {
callback(i, true);
}
}
loop();
}
Using web worker:
/***** Your worker.js *****/
this.addEventListener('message', function (e) {
var i = 0;
while (i < e.data.target) {
i++;
}
this.postMessage({
done: true,
currentI: i,
caller: e.data.caller
});
});
/***** Your main program *****/
//begin the program
console.log('begin');
nonBlockingIncrement(100, function (currentI, done) {
if (done) {
console.log('0 incremented to ' + currentI);
}
});
console.log('do more stuff');
// Create web worker and callback register
var worker = new Worker('./worker.js'),
callbacks = {};
worker.addEventListener('message', function (e) {
callbacks[e.data.caller](e.data.currentI, e.data.done);
});
//define the slow function; this would normally be a server call
function nonBlockingIncrement(n, callback){
const caller = 'nonBlockingIncrement';
callbacks[caller] = callback;
worker.postMessage({
target: n,
caller: caller
});
}
You cannot run the web worker solution as it requires a separate worker.js file to host worker logic.
You cannot execute Two loops at the same time, remember that JS is single thread.
So, doing this will never work
function loopTest() {
var test = 0
for (var i; i<=100000000000, i++) {
test +=1
}
return test
}
setTimeout(()=>{
//This will block everything, so the second won't start until this loop ends
console.log(loopTest())
}, 1)
setTimeout(()=>{
console.log(loopTest())
}, 1)
If you want to achieve multi thread you have to use Web Workers, but they have to have a separated js file and you only can pass objects to them.
But, I've managed to use Web Workers without separated files by genering Blob files and i can pass them callback functions too.
//A fileless Web Worker
class ChildProcess {
//#param {any} ags, Any kind of arguments that will be used in the callback, functions too
constructor(...ags) {
this.args = ags.map(a => (typeof a == 'function') ? {type:'fn', fn:a.toString()} : a)
}
//#param {function} cb, To be executed, the params must be the same number of passed in the constructor
async exec(cb) {
var wk_string = this.worker.toString();
wk_string = wk_string.substring(wk_string.indexOf('{') + 1, wk_string.lastIndexOf('}'));
var wk_link = window.URL.createObjectURL( new Blob([ wk_string ]) );
var wk = new Worker(wk_link);
wk.postMessage({ callback: cb.toString(), args: this.args });
var resultado = await new Promise((next, error) => {
wk.onmessage = e => (e.data && e.data.error) ? error(e.data.error) : next(e.data);
wk.onerror = e => error(e.message);
})
wk.terminate(); window.URL.revokeObjectURL(wk_link);
return resultado
}
worker() {
onmessage = async function (e) {
try {
var cb = new Function(`return ${e.data.callback}`)();
var args = e.data.args.map(p => (p.type == 'fn') ? new Function(`return ${p.fn}`)() : p);
try {
var result = await cb.apply(this, args); //If it is a promise or async function
return postMessage(result)
} catch (e) { throw new Error(`CallbackError: ${e}`) }
} catch (e) { postMessage({error: e.message}) }
}
}
}
setInterval(()=>{console.log('Not blocked code ' + Math.random())}, 1000)
console.log("starting blocking synchronous code in Worker")
console.time("\nblocked");
var proc = new ChildProcess(blockCpu, 43434234);
proc.exec(function(block, num) {
//This will block for 10 sec, but
block(10000) //This blockCpu function is defined below
return `\n\nbla bla ${num}\n` //Captured in the resolved promise
}).then(function (result){
console.timeEnd("\nblocked")
console.log("End of blocking code", result)
})
.catch(function(error) { console.log(error) })
//random blocking function
function blockCpu(ms) {
var now = new Date().getTime();
var result = 0
while(true) {
result += Math.random() * Math.random();
if (new Date().getTime() > now +ms)
return;
}
}
For very long tasks, a Web-Worker should be preferred, however for small-enough tasks (< a couple of seconds) or for when you can't move the task to a Worker (e.g because you needs to access the DOM or whatnot, Alnitak's solution of splitting the code in chunks is the way to go.
Nowadays, this can be rewritten in a cleaner way thanks to async/await syntax.
Also, instead of waiting for setTimeout() (which is delayed to at least 1ms in node-js and to 4ms everywhere after the 5th recursive call), it's better to use a MessageChannel.
So this gives us
const waitForNextTask = () => {
const { port1, port2 } = waitForNextTask.channel ??= new MessageChannel();
return new Promise( (res) => {
port1.addEventListener("message", () => res(), { once: true } );
port1.start();
port2.postMessage("");
} );
};
async function doSomethingSlow() {
const chunk_size = 10000;
// do something slow, like counting from 0 to Infinity
for (let i = 0; i < Infinity; i++ ) {
// we've done a full chunk, let the event-loop loop
if( i % chunk_size === 0 ) {
log.textContent = i; // just for demo, to check we're really doing something
await waitForNextTask();
}
}
console.log("Ah! Did it!");
}
console.log("starting my slow computation");
doSomethingSlow();
console.log("started my slow computation");
setTimeout(() => console.log("my slow computation is probably still running"), 5000);
<pre id="log"></pre>
Using ECMA async function it's very easy to write non-blocking async code, even if it performs CPU-bound operations. Let's do this on a typical academic task - Fibonacci calculation for the incredible huge value.
All you need is to insert an operation that allows the event loop to be reached from time to time. Using this approach, you will never freeze the user interface or I/O.
Basic implementation:
const fibAsync = async (n) => {
let lastTimeCalled = Date.now();
let a = 1n,
b = 1n,
sum,
i = n - 2;
while (i-- > 0) {
sum = a + b;
a = b;
b = sum;
if (Date.now() - lastTimeCalled > 15) { // Do we need to poll the eventloop?
lastTimeCalled = Date.now();
await new Promise((resolve) => setTimeout(resolve, 0)); // do that
}
}
return b;
};
And now we can use it (Live Demo):
let ticks = 0;
console.warn("Calulation started");
fibAsync(100000)
.then((v) => console.log(`Ticks: ${ticks}\nResult: ${v}`), console.warn)
.finally(() => {
clearTimeout(timer);
});
const timer = setInterval(
() => console.log("timer tick - eventloop is not freezed", ticks++),
0
);
As we can see, the timer is running normally, which indicates the event loop is not blocking.
I published an improved implementation of these helpers as antifreeze2 npm package. It uses setImmediate internally, so to get the maximum performance you need to import setImmediate polyfill for environments without native support.
Live Demo
import { antifreeze, isNeeded } from "antifreeze2";
const fibAsync = async (n) => {
let a = 1n,
b = 1n,
sum,
i = n - 2;
while (i-- > 0) {
sum = a + b;
a = b;
b = sum;
if (isNeeded()) {
await antifreeze();
}
}
return b;
};
If you are using jQuery, I created a deferred implementation of Alnitak's answer
function deferredEach (arr, batchSize) {
var deferred = $.Deferred();
var index = 0;
function chunk () {
var lastIndex = Math.min(index + batchSize, arr.length);
for(;index<lastIndex;index++){
deferred.notify(index, arr[index]);
}
if (index >= arr.length) {
deferred.resolve();
} else {
setTimeout(chunk, 0);
}
};
setTimeout(chunk, 0);
return deferred.promise();
}
Then you'll be able to use the returned promise to manage the progress and done callback:
var testArray =["Banana", "Orange", "Apple", "Mango"];
deferredEach(testArray, 2).progress(function(index, item){
alert(item);
}).done(function(){
alert("Done!");
})
I managed to get an extremely short algorithm using functions. Here is an example:
let l=($,a,f,r)=>{f(r||0),$((r=a(r||0))||0)&&l($,a,f,r)};
l
(i => i < 4, i => i+1, console.log)
/*
output:
0
1
2
3
*/
I know this looks very complicated, so let me explain what is really going on here.
Here is a slightly simplified version of the l function.
let l_smpl = (a,b,c,d) => {c(d||0);d=b(d||0),a(d||0)&&l_smpl(a,b,c,d)||0}
First step in the loop, l_smpl calls your callback and passes in d - the index. If d is undefined, as it would be on the first call, it changes it to 0.
Next, it updates d by calling your updater function and setting d to the result. In our case, the updater function would add 1 to the index.
The next step checks if your condition is met by calling the first function and checking if the value is true meaning the loop is not done. If so, it calls the function again, or otherwise, it returns 0 to end the loop.
Working code: in Chrome, Firefox
let sleep = function (ms) {
return new Promise(resolve => setTimeout(resolve, ms))
};
And somewhere in my function i use async,await to make the delay synchronous
function updateHandler(newTags, tagName, contentIds) {
let deferred = Q.defer(),
counter = 0,
failedIDS = [],
data = {};
data["contentIds"] = contentIds;
data["failedIDS"] = failedIDS;
if (contentIds.length === 0) {
return Promise.resolve(data);
}
//aync and await is here
_.forEach(contentIds, async function (contentId) {
//wait for some time and continue
await sleep(150);
let tags = [], activity;
//API hits..
osapi.jive.core.get({
v: "v3",
href: "/contents/" + contentId + ""
}).execute(function (content) {
tags = content.tags;
activity = content["updated"];
content["tags"] = _.union(tags, newTags);
osapi.jive.core.put({
v: "v3",
href: "/contents/" + contentId + "",
body: content,
"minor": "true",
"updated": activity
}).execute(function (response) {
counter++;
if (response.error) {
failedIDS.push(contentId);
}
if (counter === contentIds.length) {
deferred.resolve(data);
}
}, function (error) {
counter++;
failedIDS.push(contentId);
if (counter === contentIds.length) {
deferred.resolve(data);
}
}
);
})
});
return deferred.promise;
};
So a 0.15 seconds is must for this api hit to work and update all the items.
Since async and await won't work in IE, I wanted to write a basic wait(ms) function which waits for 0.15 seconds.
Note: So, without sleep() function, above loop works fine for the first iteration and fails for the second iteration and terminates the code execution. SO a must 0.15 seconds delay for each iteration is needed, this is the product limitation.
setTimeout() is asynchronous.. so i didn't use it.
Below code works for me.. But it's not what I want, because the browser runs out of memory and more CPU utilization, expensive..
function wait(ms) {
console.log("started............");
var start = Date.now(),
now = start;
while (now - start < ms) {
now = Date.now();
}
console.log("finished............");
}
Question: I want to have atleast 0.15 seconds delay for each iteration, how can I achieve it.
++ I tried the following way, picture here. Successfully updates only 16 to 19 contents, out of 100 iterable items and then throws the same error as it does when without sleep() function.
Say I need to run this request function every 150ms:
const request = () => new Promise(res => setTimeout(() => { console.log('done'); res() }, 1000))
//
Then I can use setTimeout recursively to add a delay between each request:
let counter = 0;
// this handler will be passed into a setTimeout
// to kick off the whole thing
const handler = () => {
console.log(counter);
// request api thing
request().then(() => {
counter++;
if (counter === 100) return;
setTimeout(handler, 150) // remove this
})
}
// kick off
setTimeout(handler, 150)
It makes sure each request is finished before waiting to run the next one.
I have javascript function like this:
function myFunction(number) {
var x=number;
...
... more initializations
//here need to wait until flag==true
while(flag==false)
{}
...
... do something
}
The problem is that the javascript is stuck in the while and stuck my program. so my question is how can I wait in the middle of the function until flag is true without "busy-wait"?
Javascript is single threaded, hence the page blocking behaviour. You can use the deferred/promise approach suggested by others. The most basic way would be to use window.setTimeout. E.g.
function checkFlag() {
if(flag === false) {
window.setTimeout(checkFlag, 100); /* this checks the flag every 100 milliseconds*/
} else {
/* do something*/
}
}
checkFlag();
Here is a good tutorial with further explanation: Tutorial
EDIT
As others pointed out, the best way would be to re-structure your code to use callbacks. However, this answer should give you an idea how you can 'simulate' an asynchronous behaviour with window.setTimeout.
You created an infinite loop where the flag value that terminates the loop can never be changed by code outside this loop because no code outside the loop ever gets to run - thus this will never work.
Because javascript in a browser is single threaded (except for webworkers which aren't involved here) and one thread of javascript execution runs to completion before another can run, your statement:
// this won't work!
while(flag==false) {}
will simply run forever (or until the browser complains about a non-responsive javascript loop), the page will appear to be hung and no other javascript will ever get a chance to run, thus the flag's value can never be changed by code outside this loop.
For a little more explanation, Javascript is an event driven language. That means that it runs a piece of Javascript until it returns control back to the interpreter. Then, only when it returns back to the interpreter, Javascript gets the next event from the event queue and runs it.
All things like timers and network events run through the event queue. So, when a timer fires or a network request arrives, it does not ever "interrupt" the currently running Javascript. Instead, an event gets put in the Javascript event queue and then, when the currently running Javascript finishes, the next event is pulled from the event queue and it gets its turn to run.
So, when you do an infinite loop such as while(flag==false) {}, the currently running Javascript never finishes and thus the next event is never pulled from the event queue and thus the value of flag never gets changed. They key here is that Javascript is not interrupt driven. When a timer fires, it does not interrupt the currently running Javascript, run some other Javascript and then let the currently running Javascript continue. It just gets put in the event queue waiting until the currently running Javascript is done to get its turn to run.
What you need to do is rethink how your code works and find a different way to trigger whatever code you want to run when the flag value changes. Javascript is designed as an event-driven language. So, what you need to do is figure out what events you can register an interest in so you can either listen for the event that might cause the flag to change and you can examine the flag on that event or you can trigger your own event from whatever code might change the flag or you can implement a callback function that whatever code changes that flag can call your callback whenever the piece of code responsible for changing the flag value would change it's value to true, it just calls the callback function and thus your code that wants to run when the flag gets set to true will get to run at the right time. This is much, much more efficient than trying to use some sort of timer to constantly check the flag value.
function codeThatMightChangeFlag(callback) {
// do a bunch of stuff
if (condition happens to change flag value) {
// call the callback to notify other code
callback();
}
}
Solution using Promise, async\await and EventEmitter which allows to react immediate on flag change without any kind of loops at all
const EventEmitter = require('events');
const bus = new EventEmitter();
let lock = false;
async function lockable() {
if (lock) await new Promise(resolve => bus.once('unlocked', resolve));
....
lock = true;
...some logic....
lock = false;
bus.emit('unlocked');
}
EventEmitter is builtin in node. In browser you shall need to include it by your own, for example using this package: https://www.npmjs.com/package/eventemitter3
ES6 with Async / Await ,
let meaningOfLife = false;
async function waitForMeaningOfLife(){
while (true){
if (meaningOfLife) { console.log(42); return };
await null; // prevents app from hanging
}
}
waitForMeaningOfLife();
setTimeout(()=>meaningOfLife=true,420)
Modern solution using Promise
myFunction() in the original question can be modified as follows
async function myFunction(number) {
var x=number;
...
... more initializations
await until(_ => flag == true);
...
... do something
}
where until() is this utility function
function until(conditionFunction) {
const poll = resolve => {
if(conditionFunction()) resolve();
else setTimeout(_ => poll(resolve), 400);
}
return new Promise(poll);
}
Some references to async/await and arrow functions are in a similar post:
https://stackoverflow.com/a/52652681/209794
function waitFor(condition, callback) {
if(!condition()) {
console.log('waiting');
window.setTimeout(waitFor.bind(null, condition, callback), 100); /* this checks the flag every 100 milliseconds*/
} else {
console.log('done');
callback();
}
}
Use:
waitFor(() => window.waitForMe, () => console.log('got you'))
I solved this issue by implementing the method below.
const waitUntil = (condition, checkInterval=100) => {
return new Promise(resolve => {
let interval = setInterval(() => {
if (!condition()) return;
clearInterval(interval);
resolve();
}, checkInterval)
})
}
Now, whenever you want to wait until a certain condition is met you can call it like this.
await waitUntil(() => /* your condition */)
const waitUntil = (condition, checkInterval=100) => {
return new Promise(resolve => {
let interval = setInterval(() => {
if (!condition()) return;
clearInterval(interval);
resolve();
}, checkInterval)
})
}
async function start() {
let flag = false;
console.log('wait 5 sec');
setTimeout(()=> {flag=true}, 5000); // set flag=true after 5 seconds
await waitUntil(() => flag==true ); // wait
console.log('do something when flag is true...');
}
start();
With Ecma Script 2017 You can use async-await and while together to do that
And while will not crash or lock the program even variable never be true
//First define some delay function which is called from async function
function __delay__(timer) {
return new Promise(resolve => {
timer = timer || 2000;
setTimeout(function () {
resolve();
}, timer);
});
};
//Then Declare Some Variable Global or In Scope
//Depends on you
var flag = false;
//And define what ever you want with async fuction
async function some() {
while (!flag)
await __delay__(1000);
//...code here because when Variable = true this function will
};
For iterating over ($.each) objects and executing a longish-running operation (containing nested ajax sync calls) on each object:
I first set a custom done=false property on each.
Then, in a recursive function, set each done=true and continued using setTimeout. (It's an operation meant to stop all other UI, show a progress bar and block all other use so I forgave myself for the sync calls.)
function start()
{
GlobalProducts = getproductsfromsomewhere();
$.each(GlobalProducts, function(index, product) {
product["done"] = false;
});
DoProducts();
}
function DoProducts()
{
var doneProducts = Enumerable.From(GlobalProducts).Where("$.done == true").ToArray(); //linqjs
//update progress bar here
var nextProduct = Enumerable.From(GlobalProducts).Where("$.done == false").First();
if (nextProduct) {
nextProduct.done = true;
Me.UploadProduct(nextProduct.id); //does the long-running work
setTimeout(Me.UpdateProducts, 500)
}
}
If you are allowed to use: async/await on your code, you can try this one:
const waitFor = async (condFunc: () => boolean) => {
return new Promise((resolve) => {
if (condFunc()) {
resolve();
}
else {
setTimeout(async () => {
await waitFor(condFunc);
resolve();
}, 100);
}
});
};
const myFunc = async () => {
await waitFor(() => (window as any).goahead === true);
console.log('hello world');
};
myFunc();
Demo here:
https://stackblitz.com/edit/typescript-bgtnhj?file=index.ts
On the console, just copy/paste: goahead = true.
TMCDR; (= "too much code... didn't read")
Simplest in terms of readability of the calling code and conciseness of the implementing code:
const until = (predFn) => {
const poll = (done) => (predFn() ? done() : setTimeout(() => poll(done), 500));
return new Promise(poll);
};
Example calling code:
await until(() => { myBankBalance > 1000000 });
More detailed example:
https://replit.com/#SteveChambers1/Javascript-until-function?v=1
The cleanest solution (improvement of #tdxius solution) based on controlled time interval loop, promise and timeout to reject the promise and clear intervals in case condition isn't met in a given time
const waitUntil = (condition) => {
return new Promise((resolve, reject) => {
const interval = setInterval(() => {
if (!condition()) {
return;
}
clearInterval(interval);
resolve();
}, 100);
setTimeout(() => {
clearInterval(interval);
reject('your error msg');
}, 5000);
});
};
Now, whenever you want to wait until a certain condition is met, you can call it like this.
waitUntil(CONDITION_FUNCTION)
.then(() => DO_SOMETHING)
.catch((YOUR_ERROR_MSG) => console.warn(YOUR_ERROR_MSG))
using non blocking javascript with EventTarget API
In my example, i need to wait for a callback before to use it. I have no idea when this callback is set. It can be before of after i need to execute it. And i can need to call it several time (everything async)
// bus to pass event
const bus = new EventTarget();
// it's magic
const waitForCallback = new Promise((resolve, reject) => {
bus.addEventListener("initialized", (event) => {
resolve(event.detail);
});
});
// LET'S TEST IT !
// launch before callback has been set
waitForCallback.then((callback) => {
console.log(callback("world"));
});
// async init
setTimeout(() => {
const callback = (param) => { return `hello ${param.toString()}`; }
bus.dispatchEvent(new CustomEvent("initialized", {detail: callback}));
}, 500);
// launch after callback has been set
setTimeout(() => {
waitForCallback.then((callback) => {
console.log(callback("my little pony"));
});
}, 1000);
Did anyone ever think of just doing this?
function resolveAfter2Seconds() {
return new Promise(resolve => {
setTimeout(() => {
resolve();
}, 2000);
});
}
function myFunction(number) {
var x=number;
...
... more initializations
//here need to wait until flag==true
while(flag==false)
{
await resolveAfter2Seconds();
}
...
... do something
}
I tried to used #Kiran approach like follow:
checkFlag: function() {
var currentObject = this;
if(flag == false) {
setTimeout(currentObject.checkFlag, 100);
} else {
/* do something*/
}
}
(framework that I am using force me to define functions this way).
But without success because when execution come inside checkFlag function second time, this is not my object it is Window.
So, I finished with code below
checkFlag: function() {
var worker = setInterval (function(){
if(flag == true){
/* do something*/
clearInterval (worker);
}
},100);
}
there is a node package delay very easy to use
const delay = require('delay');
(async () => {
bar();
await delay(100);
// Executed 100 milliseconds later
baz();
})();
I took an approach along the lines of the callback solutions here, but tried to make it a bit more generic. The idea is you add functions that you need to execute after something changes to a queue. When the thing happens, you then loop through the queue, call the functions and empty the queue.
Add function to queue:
let _queue = [];
const _addToQueue = (funcToQ) => {
_queue.push(funcToQ);
}
Execute and flush the queue:
const _runQueue = () => {
if (!_queue || !_queue.length) {
return;
}
_queue.forEach(queuedFunc => {
queuedFunc();
});
_queue = [];
}
And when you invoke _addToQueue you'll want to wrap the callback:
_addToQueue(() => methodYouWantToCallLater(<pass any args here like you normally would>));
When you've met the condition, call _runQueue()
This was useful for me because I had several things that needed to wait on the same condition. And it decouples the detection of the condition from whatever needs to be executed when that condition is hit.
Try avoid while loop as it could be blocking your code, use async and promises.
Just wrote this library:
https://www.npmjs.com/package/utilzed
There is a function waitForTrue
import utilzed from 'utilzed'
const checkCondition = async () => {
// anything that you are polling for to be expecting to be true
const response = await callSomeExternalApi();
return response.success;
}
// this will waitForTrue checkCondition to be true
// checkCondition will be called every 100ms
const success = await utilzed.waitForTrue(100, checkCondition, 1000);
if (success) {
// Meaning checkCondition function returns true before 1000 ms
return;
}
// meaning after 1000ms the checkCondition returns false still
// handle unsuccessful "poll for true"
Similar to Lightbeard's answer, I use the following approach
function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms))
}
async function until(fn) {
while (!fn()) {
await sleep(0)
}
}
async function myFunction(number) {
let x = number
...
... more initialization
await until(() => flag == true)
...
... do something
}
//function a(callback){
setTimeout(function() {
console.log('Hi I am order 1');
}, 3000);
// callback();
//}
//function b(callback){
setTimeout(function() {
console.log('Hi I am order 2');
}, 2000);
// callback();
//}
//function c(callback){
setTimeout(function() {
console.log('Hi I am order 3');
}, 1000);
// callback();
//}
/*function d(callback){
a(function(){
b(function(){
c(callback);
});
});
}
d();*/
async function funa(){
var pr1=new Promise((res,rej)=>{
setTimeout(()=>res("Hi4 I am order 1"),3000)
})
var pr2=new Promise((res,rej)=>{
setTimeout(()=>res("Hi4 I am order 2"),2000)
})
var pr3=new Promise((res,rej)=>{
setTimeout(()=>res("Hi4 I am order 3"),1000)
})
var res1 = await pr1;
var res2 = await pr2;
var res3 = await pr3;
console.log(res1,res2,res3);
console.log(res1);
console.log(res2);
console.log(res3);
}
funa();
async function f1(){
await new Promise(r=>setTimeout(r,3000))
.then(()=>console.log('Hi3 I am order 1'))
return 1;
}
async function f2(){
await new Promise(r=>setTimeout(r,2000))
.then(()=>console.log('Hi3 I am order 2'))
return 2;
}
async function f3(){
await new Promise(r=>setTimeout(r,1000))
.then(()=>console.log('Hi3 I am order 3'))
return 3;
}
async function finaloutput2(arr){
return await Promise.all([f3(),f2(),f1()]);
}
//f1().then(f2().then(f3()));
//f3().then(f2().then(f1()));
//finaloutput2();
//var pr1=new Promise(f3)
async function f(){
console.log("makesure");
var pr=new Promise((res,rej)=>{
setTimeout(function() {
console.log('Hi2 I am order 1');
}, 3000);
});
var result=await pr;
console.log(result);
}
// f();
async function g(){
console.log("makesure");
var pr=new Promise((res,rej)=>{
setTimeout(function() {
console.log('Hi2 I am order 2');
}, 2000);
});
var result=await pr;
console.log(result);
}
// g();
async function h(){
console.log("makesure");
var pr=new Promise((res,rej)=>{
setTimeout(function() {
console.log('Hi2 I am order 3');
}, 1000);
});
var result=await pr;
console.log(result);
}
async function finaloutput(arr){
return await Promise.all([f(),g(),h()]);
}
//finaloutput();
//h();
In my example, I log a new counter value every second:
var promises_arr = [];
var new_cntr_val = 0;
// fill array with promises
for (let seconds = 1; seconds < 10; seconds++) {
new_cntr_val = new_cntr_val + 5; // count to 50
promises_arr.push(new Promise(function (resolve, reject) {
// create two timeouts: one to work and one to resolve the promise
setTimeout(function(cntr) {
console.log(cntr);
}, seconds * 1000, new_cntr_val); // feed setTimeout the counter parameter
setTimeout(resolve, seconds * 1000);
}));
}
// wait for promises to finish
Promise.all(promises_arr).then(function (values) {
console.log("all promises have returned");
});
Modern and simple solution
async function waitUntil(condition, time = 100) {
while (!condition()) {
await new Promise((resolve) => setTimeout(resolve, time));
}
}
Usage
async function foo() {
await waitUntil(() => flag === true);
console.log('condition is met!');
}
Inspired by jfriend00, this worked for me
const seconds = new Date();
// wait 5 seconds for flag to become true
const waitTime = 5
const extraSeconds = seconds.setSeconds(seconds.getSeconds() + waitTime);
while (Date.now() < extraSeconds) {
// break when flag is false
if (flag === false) break;
}
I have javascript function like this:
function myFunction(number) {
var x=number;
...
... more initializations
//here need to wait until flag==true
while(flag==false)
{}
...
... do something
}
The problem is that the javascript is stuck in the while and stuck my program. so my question is how can I wait in the middle of the function until flag is true without "busy-wait"?
Javascript is single threaded, hence the page blocking behaviour. You can use the deferred/promise approach suggested by others. The most basic way would be to use window.setTimeout. E.g.
function checkFlag() {
if(flag === false) {
window.setTimeout(checkFlag, 100); /* this checks the flag every 100 milliseconds*/
} else {
/* do something*/
}
}
checkFlag();
Here is a good tutorial with further explanation: Tutorial
EDIT
As others pointed out, the best way would be to re-structure your code to use callbacks. However, this answer should give you an idea how you can 'simulate' an asynchronous behaviour with window.setTimeout.
You created an infinite loop where the flag value that terminates the loop can never be changed by code outside this loop because no code outside the loop ever gets to run - thus this will never work.
Because javascript in a browser is single threaded (except for webworkers which aren't involved here) and one thread of javascript execution runs to completion before another can run, your statement:
// this won't work!
while(flag==false) {}
will simply run forever (or until the browser complains about a non-responsive javascript loop), the page will appear to be hung and no other javascript will ever get a chance to run, thus the flag's value can never be changed by code outside this loop.
For a little more explanation, Javascript is an event driven language. That means that it runs a piece of Javascript until it returns control back to the interpreter. Then, only when it returns back to the interpreter, Javascript gets the next event from the event queue and runs it.
All things like timers and network events run through the event queue. So, when a timer fires or a network request arrives, it does not ever "interrupt" the currently running Javascript. Instead, an event gets put in the Javascript event queue and then, when the currently running Javascript finishes, the next event is pulled from the event queue and it gets its turn to run.
So, when you do an infinite loop such as while(flag==false) {}, the currently running Javascript never finishes and thus the next event is never pulled from the event queue and thus the value of flag never gets changed. They key here is that Javascript is not interrupt driven. When a timer fires, it does not interrupt the currently running Javascript, run some other Javascript and then let the currently running Javascript continue. It just gets put in the event queue waiting until the currently running Javascript is done to get its turn to run.
What you need to do is rethink how your code works and find a different way to trigger whatever code you want to run when the flag value changes. Javascript is designed as an event-driven language. So, what you need to do is figure out what events you can register an interest in so you can either listen for the event that might cause the flag to change and you can examine the flag on that event or you can trigger your own event from whatever code might change the flag or you can implement a callback function that whatever code changes that flag can call your callback whenever the piece of code responsible for changing the flag value would change it's value to true, it just calls the callback function and thus your code that wants to run when the flag gets set to true will get to run at the right time. This is much, much more efficient than trying to use some sort of timer to constantly check the flag value.
function codeThatMightChangeFlag(callback) {
// do a bunch of stuff
if (condition happens to change flag value) {
// call the callback to notify other code
callback();
}
}
Solution using Promise, async\await and EventEmitter which allows to react immediate on flag change without any kind of loops at all
const EventEmitter = require('events');
const bus = new EventEmitter();
let lock = false;
async function lockable() {
if (lock) await new Promise(resolve => bus.once('unlocked', resolve));
....
lock = true;
...some logic....
lock = false;
bus.emit('unlocked');
}
EventEmitter is builtin in node. In browser you shall need to include it by your own, for example using this package: https://www.npmjs.com/package/eventemitter3
ES6 with Async / Await ,
let meaningOfLife = false;
async function waitForMeaningOfLife(){
while (true){
if (meaningOfLife) { console.log(42); return };
await null; // prevents app from hanging
}
}
waitForMeaningOfLife();
setTimeout(()=>meaningOfLife=true,420)
Modern solution using Promise
myFunction() in the original question can be modified as follows
async function myFunction(number) {
var x=number;
...
... more initializations
await until(_ => flag == true);
...
... do something
}
where until() is this utility function
function until(conditionFunction) {
const poll = resolve => {
if(conditionFunction()) resolve();
else setTimeout(_ => poll(resolve), 400);
}
return new Promise(poll);
}
Some references to async/await and arrow functions are in a similar post:
https://stackoverflow.com/a/52652681/209794
function waitFor(condition, callback) {
if(!condition()) {
console.log('waiting');
window.setTimeout(waitFor.bind(null, condition, callback), 100); /* this checks the flag every 100 milliseconds*/
} else {
console.log('done');
callback();
}
}
Use:
waitFor(() => window.waitForMe, () => console.log('got you'))
I solved this issue by implementing the method below.
const waitUntil = (condition, checkInterval=100) => {
return new Promise(resolve => {
let interval = setInterval(() => {
if (!condition()) return;
clearInterval(interval);
resolve();
}, checkInterval)
})
}
Now, whenever you want to wait until a certain condition is met you can call it like this.
await waitUntil(() => /* your condition */)
const waitUntil = (condition, checkInterval=100) => {
return new Promise(resolve => {
let interval = setInterval(() => {
if (!condition()) return;
clearInterval(interval);
resolve();
}, checkInterval)
})
}
async function start() {
let flag = false;
console.log('wait 5 sec');
setTimeout(()=> {flag=true}, 5000); // set flag=true after 5 seconds
await waitUntil(() => flag==true ); // wait
console.log('do something when flag is true...');
}
start();
With Ecma Script 2017 You can use async-await and while together to do that
And while will not crash or lock the program even variable never be true
//First define some delay function which is called from async function
function __delay__(timer) {
return new Promise(resolve => {
timer = timer || 2000;
setTimeout(function () {
resolve();
}, timer);
});
};
//Then Declare Some Variable Global or In Scope
//Depends on you
var flag = false;
//And define what ever you want with async fuction
async function some() {
while (!flag)
await __delay__(1000);
//...code here because when Variable = true this function will
};
For iterating over ($.each) objects and executing a longish-running operation (containing nested ajax sync calls) on each object:
I first set a custom done=false property on each.
Then, in a recursive function, set each done=true and continued using setTimeout. (It's an operation meant to stop all other UI, show a progress bar and block all other use so I forgave myself for the sync calls.)
function start()
{
GlobalProducts = getproductsfromsomewhere();
$.each(GlobalProducts, function(index, product) {
product["done"] = false;
});
DoProducts();
}
function DoProducts()
{
var doneProducts = Enumerable.From(GlobalProducts).Where("$.done == true").ToArray(); //linqjs
//update progress bar here
var nextProduct = Enumerable.From(GlobalProducts).Where("$.done == false").First();
if (nextProduct) {
nextProduct.done = true;
Me.UploadProduct(nextProduct.id); //does the long-running work
setTimeout(Me.UpdateProducts, 500)
}
}
If you are allowed to use: async/await on your code, you can try this one:
const waitFor = async (condFunc: () => boolean) => {
return new Promise((resolve) => {
if (condFunc()) {
resolve();
}
else {
setTimeout(async () => {
await waitFor(condFunc);
resolve();
}, 100);
}
});
};
const myFunc = async () => {
await waitFor(() => (window as any).goahead === true);
console.log('hello world');
};
myFunc();
Demo here:
https://stackblitz.com/edit/typescript-bgtnhj?file=index.ts
On the console, just copy/paste: goahead = true.
TMCDR; (= "too much code... didn't read")
Simplest in terms of readability of the calling code and conciseness of the implementing code:
const until = (predFn) => {
const poll = (done) => (predFn() ? done() : setTimeout(() => poll(done), 500));
return new Promise(poll);
};
Example calling code:
await until(() => { myBankBalance > 1000000 });
More detailed example:
https://replit.com/#SteveChambers1/Javascript-until-function?v=1
The cleanest solution (improvement of #tdxius solution) based on controlled time interval loop, promise and timeout to reject the promise and clear intervals in case condition isn't met in a given time
const waitUntil = (condition) => {
return new Promise((resolve, reject) => {
const interval = setInterval(() => {
if (!condition()) {
return;
}
clearInterval(interval);
resolve();
}, 100);
setTimeout(() => {
clearInterval(interval);
reject('your error msg');
}, 5000);
});
};
Now, whenever you want to wait until a certain condition is met, you can call it like this.
waitUntil(CONDITION_FUNCTION)
.then(() => DO_SOMETHING)
.catch((YOUR_ERROR_MSG) => console.warn(YOUR_ERROR_MSG))
using non blocking javascript with EventTarget API
In my example, i need to wait for a callback before to use it. I have no idea when this callback is set. It can be before of after i need to execute it. And i can need to call it several time (everything async)
// bus to pass event
const bus = new EventTarget();
// it's magic
const waitForCallback = new Promise((resolve, reject) => {
bus.addEventListener("initialized", (event) => {
resolve(event.detail);
});
});
// LET'S TEST IT !
// launch before callback has been set
waitForCallback.then((callback) => {
console.log(callback("world"));
});
// async init
setTimeout(() => {
const callback = (param) => { return `hello ${param.toString()}`; }
bus.dispatchEvent(new CustomEvent("initialized", {detail: callback}));
}, 500);
// launch after callback has been set
setTimeout(() => {
waitForCallback.then((callback) => {
console.log(callback("my little pony"));
});
}, 1000);
Did anyone ever think of just doing this?
function resolveAfter2Seconds() {
return new Promise(resolve => {
setTimeout(() => {
resolve();
}, 2000);
});
}
function myFunction(number) {
var x=number;
...
... more initializations
//here need to wait until flag==true
while(flag==false)
{
await resolveAfter2Seconds();
}
...
... do something
}
I tried to used #Kiran approach like follow:
checkFlag: function() {
var currentObject = this;
if(flag == false) {
setTimeout(currentObject.checkFlag, 100);
} else {
/* do something*/
}
}
(framework that I am using force me to define functions this way).
But without success because when execution come inside checkFlag function second time, this is not my object it is Window.
So, I finished with code below
checkFlag: function() {
var worker = setInterval (function(){
if(flag == true){
/* do something*/
clearInterval (worker);
}
},100);
}
there is a node package delay very easy to use
const delay = require('delay');
(async () => {
bar();
await delay(100);
// Executed 100 milliseconds later
baz();
})();
I took an approach along the lines of the callback solutions here, but tried to make it a bit more generic. The idea is you add functions that you need to execute after something changes to a queue. When the thing happens, you then loop through the queue, call the functions and empty the queue.
Add function to queue:
let _queue = [];
const _addToQueue = (funcToQ) => {
_queue.push(funcToQ);
}
Execute and flush the queue:
const _runQueue = () => {
if (!_queue || !_queue.length) {
return;
}
_queue.forEach(queuedFunc => {
queuedFunc();
});
_queue = [];
}
And when you invoke _addToQueue you'll want to wrap the callback:
_addToQueue(() => methodYouWantToCallLater(<pass any args here like you normally would>));
When you've met the condition, call _runQueue()
This was useful for me because I had several things that needed to wait on the same condition. And it decouples the detection of the condition from whatever needs to be executed when that condition is hit.
Try avoid while loop as it could be blocking your code, use async and promises.
Just wrote this library:
https://www.npmjs.com/package/utilzed
There is a function waitForTrue
import utilzed from 'utilzed'
const checkCondition = async () => {
// anything that you are polling for to be expecting to be true
const response = await callSomeExternalApi();
return response.success;
}
// this will waitForTrue checkCondition to be true
// checkCondition will be called every 100ms
const success = await utilzed.waitForTrue(100, checkCondition, 1000);
if (success) {
// Meaning checkCondition function returns true before 1000 ms
return;
}
// meaning after 1000ms the checkCondition returns false still
// handle unsuccessful "poll for true"
Similar to Lightbeard's answer, I use the following approach
function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms))
}
async function until(fn) {
while (!fn()) {
await sleep(0)
}
}
async function myFunction(number) {
let x = number
...
... more initialization
await until(() => flag == true)
...
... do something
}
//function a(callback){
setTimeout(function() {
console.log('Hi I am order 1');
}, 3000);
// callback();
//}
//function b(callback){
setTimeout(function() {
console.log('Hi I am order 2');
}, 2000);
// callback();
//}
//function c(callback){
setTimeout(function() {
console.log('Hi I am order 3');
}, 1000);
// callback();
//}
/*function d(callback){
a(function(){
b(function(){
c(callback);
});
});
}
d();*/
async function funa(){
var pr1=new Promise((res,rej)=>{
setTimeout(()=>res("Hi4 I am order 1"),3000)
})
var pr2=new Promise((res,rej)=>{
setTimeout(()=>res("Hi4 I am order 2"),2000)
})
var pr3=new Promise((res,rej)=>{
setTimeout(()=>res("Hi4 I am order 3"),1000)
})
var res1 = await pr1;
var res2 = await pr2;
var res3 = await pr3;
console.log(res1,res2,res3);
console.log(res1);
console.log(res2);
console.log(res3);
}
funa();
async function f1(){
await new Promise(r=>setTimeout(r,3000))
.then(()=>console.log('Hi3 I am order 1'))
return 1;
}
async function f2(){
await new Promise(r=>setTimeout(r,2000))
.then(()=>console.log('Hi3 I am order 2'))
return 2;
}
async function f3(){
await new Promise(r=>setTimeout(r,1000))
.then(()=>console.log('Hi3 I am order 3'))
return 3;
}
async function finaloutput2(arr){
return await Promise.all([f3(),f2(),f1()]);
}
//f1().then(f2().then(f3()));
//f3().then(f2().then(f1()));
//finaloutput2();
//var pr1=new Promise(f3)
async function f(){
console.log("makesure");
var pr=new Promise((res,rej)=>{
setTimeout(function() {
console.log('Hi2 I am order 1');
}, 3000);
});
var result=await pr;
console.log(result);
}
// f();
async function g(){
console.log("makesure");
var pr=new Promise((res,rej)=>{
setTimeout(function() {
console.log('Hi2 I am order 2');
}, 2000);
});
var result=await pr;
console.log(result);
}
// g();
async function h(){
console.log("makesure");
var pr=new Promise((res,rej)=>{
setTimeout(function() {
console.log('Hi2 I am order 3');
}, 1000);
});
var result=await pr;
console.log(result);
}
async function finaloutput(arr){
return await Promise.all([f(),g(),h()]);
}
//finaloutput();
//h();
In my example, I log a new counter value every second:
var promises_arr = [];
var new_cntr_val = 0;
// fill array with promises
for (let seconds = 1; seconds < 10; seconds++) {
new_cntr_val = new_cntr_val + 5; // count to 50
promises_arr.push(new Promise(function (resolve, reject) {
// create two timeouts: one to work and one to resolve the promise
setTimeout(function(cntr) {
console.log(cntr);
}, seconds * 1000, new_cntr_val); // feed setTimeout the counter parameter
setTimeout(resolve, seconds * 1000);
}));
}
// wait for promises to finish
Promise.all(promises_arr).then(function (values) {
console.log("all promises have returned");
});
Modern and simple solution
async function waitUntil(condition, time = 100) {
while (!condition()) {
await new Promise((resolve) => setTimeout(resolve, time));
}
}
Usage
async function foo() {
await waitUntil(() => flag === true);
console.log('condition is met!');
}
Inspired by jfriend00, this worked for me
const seconds = new Date();
// wait 5 seconds for flag to become true
const waitTime = 5
const extraSeconds = seconds.setSeconds(seconds.getSeconds() + waitTime);
while (Date.now() < extraSeconds) {
// break when flag is false
if (flag === false) break;
}