javascript return true or return false when and how to use it?

Question

So I see a lot of JavaScript code (have written some myself) that does something like

<script>
function CallSomeFunction()
{
   //function body
}

$(document).ready(function () {
 callSomeFunction();
 return false;
});

and at other times:

callSomeFunction();
return true;

Basically I've never understood the true use of the return true/false after function calls in JavaScript. I've just assumed its some kind of magic I need my functions to run well.

So please I'd like to know why? why do we use return true or return false after calling a JavaScript function?

It depends on the context. Probably is cancelling the action. AKA `onclick="return false"` stops the click from performing the default action. — epascarello, Oct 03 '13 at 18:18
Functions can return a value. Some things do something with that return value. It doesn’t really mean anything in particular on its own apart from what it says. — Ry-, Oct 03 '13 at 18:19
this question might help as well [What is the effect of adding return false to an onclick event] (http://stackoverflow.com/questions/128923/whats-the-effect-of-adding-return-false-to-an-onclick-event) — rahulmishra, Aug 06 '14 at 11:58

score 33 · Accepted Answer · answered Oct 03 '13 at 18:20

33

I think a lot of times when you see this code, it's from people who are in the habit of event handlers for forms, buttons, inputs, and things of that sort.

Basically, when you have something like:

<form onsubmit="return callSomeFunction();"></form>

or

<a href="#" onclick="return callSomeFunction();"></a>`

and callSomeFunction() returns true, then the form or a will submit, otherwise it won't.

Other more obvious general purposes for returning true or false as a result of a function are because they are expected to return a boolean.

answered Oct 03 '13 at 18:20

Eric Hotinger

8,957
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7

Thanks for passing the point across...i also found this link that gave me better understanding: http://css-tricks.com/return-false-and-prevent-default/ – oliverdejohnson Oct 03 '13 at 18:51
Is this supported by all major browsers? – RayLoveless Feb 04 '20 at 20:22

score 17 · Answer 2 · edited Oct 03 '13 at 18:32

17

Your code makes no sense, maybe because it's out of context.

If you mean code like this:

$('a').click(function () {
    callFunction();
    return false;
});

The return false will return false to the click-event. That tells the browser to stop following events, like follow a link. It has nothing to do with the previous function call. Javascript runs from top to bottom more or less, so a line cannot affect a previous line.

edited Oct 03 '13 at 18:32

Zaffy

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answered Oct 03 '13 at 18:20

3

"Javascript runs from top to bottom more or less" - except when hoisting is involved :) Doesn't apply to this answer though – Ivan Durst Jun 11 '15 at 01:38

score 14 · Answer 3 · answered Oct 03 '13 at 18:20

returning true or false indicates that whether execution should continue or stop right there. So just an example

<input type="button" onclick="return func();" />

Now if func() is defined like this

function func()
{
 // do something
return false;
}

the click event will never get executed. On the contrary if return true is written then the click event will always be executed.

score 0 · Answer 4 · answered Apr 19 '22 at 03:09

0

This works for me:

<form action="javascript:void(0);" onsubmit="return checkForm(this);">

answered Apr 19 '22 at 03:09

Andrew Tran

1

javascript return true or return false when and how to use it?

4 Answers4

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