Callback function in javascript

Question

What is the problem with this code

var a=function()
{
   setInterval(function(){document.write("a");},1000);
}

function b(callback)
{
    callback();
    alert(2);
}

b(a); // alert 2

It should not not show me the alert because the call not over yet?

setInterval is asynchronous. It schedules the execution of the function, but returns immediately. — Bergi
– Bergi, Commented Nov 13, 2012 at 11:37
I get the alert but I learn that callback its first do the setInteval and after that thae alert or that I'm wrong? — user1801625
– user1801625, Commented Nov 13, 2012 at 11:38

Gurpreet Singh · Accepted Answer · 2012-11-13 11:35:31Z

1

The code is running as expected. SetInterval doesn't hold the execution for rest of the code it fires assigned function after specified time.

So you will get alert and then document.write.

answered Nov 13, 2012 at 11:35

Gurpreet Singh

21.3k5 gold badges47 silver badges62 bronze badges

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

2 Comments

user1801625 Over a year ago

so what is the use of callback?

Gurpreet Singh Over a year ago

As I mentioned before it will be fired after '1000' ms

StuR · Accepted Answer · 2012-11-13 11:39:03Z

1

You could add the callback into your setInterval function so that it doesn't get executed until after the 1000 millisecond delay, e.g:

    var a=function(callback) {
        setInterval(function(){document.write("a"); callback(); },1000);
    }

    function b() {
        alert(2);
    }

a(b); // alert 2 AFTER the 1000 millisecond delay

answered Nov 13, 2012 at 11:39

StuR

12.3k9 gold badges47 silver badges66 bronze badges

Collectives™ on Stack Overflow

Callback function in javascript

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related