This question already has answers here:
Why doesn't setTimeout(.., 0) execute immediately?
(1 answer)
Is setTimeout a good solution to do async functions with javascript?
(3 answers)
Closed 4 years ago.
I have below code
console.log('one');
setTimeout(function() { console.log('two'); });
console.log('three');
The output of code when I run it is one, three, two
However I felt it should have been one, two, three as I haven't provided the wait time , which will set the wait time to 0 as default, i.e no waiting.
Then what is the reason that the output is one, three, two and not one, two, three.
setTimeout schedules the function for execution. That scheduler doesn't do its thing until after the current thread yields control back to the browser, e.g. after the last logging statement has executed.
Related
This question already has answers here:
Understanding the Event Loop
(4 answers)
Closed 1 year ago.
My understanding is that javascript is single-threaded, meaning it will only execute one line at a time.
For the following code, why is 'await' necessary? I think it will still execute fetch before it moves to the next line:
const res = await fetch('http://testurl.com');
Can someone explain the importance of await in single-thread languages?
Thank you
Two types of functions can be 'paused' mid-function,
Async functions
Generator functions
So while you are correct, only 1 line will be executed at a time, await basically tells Javascript:
This function is now paused, and resume this function once this promise resolves.
While the function is paused, other code can run. But the 'only 1 line of code will run'-rule still holds.
This question already has answers here:
How does setTimeout prevent potential stackoverflow
(2 answers)
Why the function called by setTimeout has no callstack limit?
(2 answers)
Closed 5 years ago.
By using javascript recursive setTimeout function, is it risky to get the stackoverflow?
By trying this example you can see in browser console that the stack grows. Why is it so?
var iteration = 0;
function bar() {
iteration++;
console.log("iteration: " + iteration);
console.trace();
if(iteration < 5){
setTimeout(bar, 5000);
}
}
bar();
By using javascript recursive setTimeout function, is it risky to get the stackoverflow?
No. setTimeout registers a handler that will get called by the browser when the timer triggers. By the time that happens, the stack has unwound (if it hadn't, the task that scheduled the timeout wouldn't have ended, and the browser's UI would be locked up waiting for it to end).
By trying this example you can see in browser console that the stack grows.
No, the stack unwinds before the handler is next called. If you're referring to the async "stack" entries that Chrome's devtools show you, those aren't the real stack, and they're a devtools artifact. (Start your timer, watch for two ticks so you see the "async" entry on the second one, then close your console, wait two more ticks, and reopen it; notice that there aren't any "async" entries — at all, not even the one you saw it log before closing the console!)
This question already has answers here:
How does setTimeout prevent potential stackoverflow
(2 answers)
Why the function called by setTimeout has no callstack limit?
(2 answers)
Closed 5 years ago.
By using javascript recursive setTimeout function, is it risky to get the stackoverflow?
By trying this example you can see in browser console that the stack grows. Why is it so?
var iteration = 0;
function bar() {
iteration++;
console.log("iteration: " + iteration);
console.trace();
if(iteration < 5){
setTimeout(bar, 5000);
}
}
bar();
By using javascript recursive setTimeout function, is it risky to get the stackoverflow?
No. setTimeout registers a handler that will get called by the browser when the timer triggers. By the time that happens, the stack has unwound (if it hadn't, the task that scheduled the timeout wouldn't have ended, and the browser's UI would be locked up waiting for it to end).
By trying this example you can see in browser console that the stack grows.
No, the stack unwinds before the handler is next called. If you're referring to the async "stack" entries that Chrome's devtools show you, those aren't the real stack, and they're a devtools artifact. (Start your timer, watch for two ticks so you see the "async" entry on the second one, then close your console, wait two more ticks, and reopen it; notice that there aren't any "async" entries — at all, not even the one you saw it log before closing the console!)
This question already has an answer here:
How can I write an async method in JavaScript when posting or looping? [closed]
(1 answer)
Closed 9 years ago.
How to run sequence functions in JavaScript:
I've 4 functions like this:
function myfunction()
{
callfunction1();
callfunction2();
}
In callfunction1:
function callfunction1()
{
callfunction3();
}
My problem is in "myfunction" when I call "callfunction1",callfunction1 is run and it call "callfunction3" but when "callfunction3" haven't finish,"callfunction2" is running.Have anyway to wait "callfunction3" finish then "callfunction2" is run ?
JavaScript is single-threaded, callfunction2 will only run after callfunction3 has compeletely finished.
However, if callfunction3 contains some AJAX or other asynchronous operation, then that will always happen after callfunction2 (because of the single-threaded thing, it can't start the asynchronous callback until after the synchronous stuff is done). Anything that relies on the result of an asynchronous function MUST either be in the function itself, or called by said function.
This question already has answers here:
What is the JavaScript version of sleep()?
(91 answers)
Closed 3 years ago.
Is there a JavaScript function that simulates the operation of the sleep function in PHP — a function that pauses code execution for x milliseconds, and then resumes where it left off?
I found some things here on Stack Overflow, but nothing useful.
You need to re-factor the code into pieces. This doesn't stop execution, it just puts a delay in between the parts.
function partA() {
...
window.setTimeout(partB,1000);
}
function partB() {
...
}
You can't (and shouldn't) block processing with a sleep function. However, you can use setTimeout to kick off a function after a delay:
setTimeout(function(){alert("hi")}, 1000);
Depending on your needs, setInterval might be useful, too.
setTimeout() function it's use to delay a process in JavaScript.
w3schools has an easy tutorial about this function.