johannes johannes - 7 months ago 12
Javascript Question

Why does returning false in they keydown callback does not stop the button click event?

I have a button and the following javascript routine.

$("button").keydown( function(key) {
switch(key.keyCode) {
case 32: //space
return false;
}
} );


as I understood it, the
return false;
would stop the keypress from being processed. So
$("button").click();
would not be called. For other keyCodes this works as expected. For example if I intercept
40
, which is the down button, the page is not scrolling.

I noticed this behaviour in firefox.

Why does the
return false;
does not stop the button click event on space? What does the javascript spec say about this?

Answer

Hope this answers your question:

<input type="button" value="Press" onkeydown="doOtherStuff(); return false;">

return false; successfully cancels an event across browsers if called at the end of an event handler attribute in the HTML. This behaviour is not formally specified anywhere as far as I know.

If you instead set an event via an event handler property on the DOM element (e.g. button.onkeydown = function(evt) {...}) or using addEventListener/attachEvent (e.g. button.addEventListener("keydown", function(evt) {...}, false)) then just returning false from that function does not work in every browser and you need to do the returnValue and preventDefault() stuff from my other answer. preventDefault is specified in the DOM 2 spec and is implemented by most mainstream modern browsers. returnValue is IE-specific.