What does "return false;" do?

ajax, javascript, jquery

Solution

What I'll write here is true for jQuery events, For vanilla javascript events read @T.J. Crowder comment at the bottom of the answer

`return false` inside a callback prevents the default behaviour. For example, in a `submit` event, it doesn't submit the form.

`return false` also stops bubbling, so the parents of the element won't know the event occurred.

`return false` is equivalent to `event.preventDefault()` + `event.stopPropagation()`

And of course, all code that exists after the `return xxx` line won't be executed. (as with all programming languages I know)

Maybe you find this helpful: Stop event bubbling - increases performance?

A "real" demo to explain the difference between `return false` and `event.preventDefault()`:

Markup:

<div id="theDiv">
    <form id="theForm" >
        <input type="submit" value="submit"/> 
    </form>
</div>​

JavaScript:

$('#theDiv').submit(function() {
    alert('DIV!');
});
$('#theForm').submit(function(e) {
    alert('FORM!');
    e.preventDefault();
});​

Now... when the user submit the form, the first handler is the form submit, which `preventDefault()` -> the form won't be submitted, but the event bubbles to the div, triggering it's submit handler.

Live DEMO

Now, if the form submit's handler would cancel the bubbling with `return false`:

$('#theDiv').submit(function() {
    alert('DIV!');
});
$('#theForm').submit(function(event) {
    alert('FORM!');
    return false;   
    // Or:
    event.preventDefault(); 
    event.stopPropagation();
});​

The div wouldn't even know there was a form submission.

Live DEMO

What does `return false` do in vanilla javascript events

return false from a DOM2 handler (`addEventListener`) does nothing at all (neither prevents the default nor stops bubbling; from a Microsoft DOM2-ish handler (`attachEvent`), it prevents the default but not bubbling; from a DOM0 handler (`onclick="return ..."`), it prevents the default (provided you include the return in the attribute) but not bubbling; from a jQuery event handler, it does both, because that's a jQuery thing. Details and live tests here – T.J. Crowder

Problem

Original source

Related problems

• event.preventDefault() vs. return false
• Stop event bubbling - increases performance?