set callback function to return value in javascript

Question

Here is my code:

function render(){
    var el;
    setTimeout(function(){
      func();
    },1000);
    return el;
  }

function func(){
    //do something here;
}

setTimeout is async, so el will be returned before execute func.I want to return el after calling func, how should I write the callback function?

Do you want the caller of render to wait until el is available (as you said el is returned from the function)? If so I'm not sure the @CD answer would work for you. — Paul Grime
– Paul Grime, Commented Apr 6, 2013 at 17:55
You can't. You'll need to rewrite your logic so the things that should depend on the return value of func are actually triggered at the end of func — Gareth
– Gareth, Commented Apr 6, 2013 at 17:56
@Gareth, got it. But not sure how to make it work. Any more details about how to do that? Thx — Yujun Wu
– Yujun Wu, Commented Apr 6, 2013 at 18:08

CD.. · Accepted Answer · 2013-04-06 18:21:28Z

3

use a callback - a function that el will be passed to:

function render(callback){
    var el;
    setTimeout(function(){
      func();
      callback(el);
    },1000);
  }

function func(){
    //do something here;
}

function elReady(el){
    // use `el`
}

So now you can use render(elReady).

edited Apr 6, 2013 at 18:21

answered Apr 6, 2013 at 17:52

CD..

74.4k25 gold badges160 silver badges170 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Yujun Wu Over a year ago

how should the callback function be? Simply function callback(el){return el;} won't work since I want render to return el. Could you elaborate a little bit?

CD.. Over a year ago

the callback should contain what ever you'd like to do with el, it will be called once el is 'ready'.

Yujun Wu Over a year ago

well my concern is the same as @PaulGrime commented above

user1106925 Over a year ago

@YujunWu: If you want a 1000ms delay, then you simply can not return the value you want from render. There's no such thing as a synchronous pause in JavaScript (at least not without blocking). You need to change your code to fit the environment, because the environment sure isn't going to change to fit your code.

user1106925 Over a year ago

+1 but it might help OP to see the callback actually being passed to render. This can be confusing at first.

Collectives™ on Stack Overflow

set callback function to return value in javascript

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related