Javascript function calling within setTimeout - which is better?

Question

I have two versions of the code. Can someone let me know which is optimal and faster?

Version 1:

function showMsg(a)
{
    alert(a);
}
function invokeShowMsg()
{
    var msg = 'hi';
    showMsg(msg);
}
window.setTimeout(invokeShowMsg,1000);

Version 2:

function showMsg(a)
{
    alert(a);
}
window.setTimeout(function(){showMsg('hi');},1000);

One more doubt, is the Version 2 way of calling called "Closure"?

What are your criteria for "optimal"? I suspect #1 is faster because it passes a reference to an already declared function rather than evaluating a function expression and passing a reference to that—but you should test it in various browsers. In any case, if execution is delayed by a minimum of 1 second, of what relevance is speed? — RobG
– RobG, Commented Jan 23, 2012 at 4:44
Since I run it in a Mobile browser, will version 2 cause any adverse impact? — thandasoru
– thandasoru, Commented Jan 23, 2012 at 4:51
You will not notice it, even if you tried. Most* JS engines compile the code. — Blender
– Blender, Commented Jan 23, 2012 at 4:56

Blender · Accepted Answer · 2012-01-23 04:52:24Z

4

As far as speed goes, you will not notice any difference between the two whatsoever, so pick what you like.

I prefer #2, as it is cleaner and keeps the syntax readable:

setTimeout(function() {
  showMsg('hi');
}, 1000);

edited Jan 23, 2012 at 4:52

answered Jan 23, 2012 at 4:39

Blender

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3 Comments

voithos Over a year ago

Is it really a closure?

Blender Over a year ago

I just say yes because it makes no difference whatsoever to me, as I haven't really found a practical use for distinguishing an anonymous function and a closure (even if I use both).

Blender Over a year ago

But +1 for actually knowing the answer. I retract my statement in shame.

ozczecho · Accepted Answer · 2012-01-23 04:39:56Z

3

Yes , version 2 is called Closure. As far as speed, they are both equivalent.

answered Jan 23, 2012 at 4:39

ozczecho

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1 Comment

thandasoru Over a year ago

Thanks, I read somewhere in Google's pages where it said version 2 (closure) is slower than version 1. I used version 2 all over my code and I don't really want to change it now..

Community · Accepted Answer · 2017-05-23 11:48:09Z

2

As @Blender said, I also prefer 2, as it doesn't pollute the global space with (semi-useless) "caller" functions. It's clean, and it simple to understand to someone who knows how setTimeout works. And as far as speed goes, there's virtually no difference. Here's a performance comparison of the two methods.

However, as far as I understand, it is not a closure. It is simply an anonymous function. In JavaScript, as in many other dynamic language, functions are first class citizens, meaning that they can be created and passed around- they are objects. However, a closure is more than just an anonymous function. The answers to this question explain what a closure is quite succinctly.

edited May 23, 2017 at 11:48

CommunityBot

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answered Jan 23, 2012 at 4:46

voithos

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1 Comment

thandasoru Over a year ago

thanks for the link.. excellent description provided there :-)

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