views:

593

answers:

3

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 intercept40, 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?

A: 

could it be because you have "return fale" instead of "return false"? O_o

Willson Haw
No in my actual code I have `false` instead of `fale`. It's a type here ;-)
johannes
A: 

First, if you're detecting a printable character such as space, you would be better off with the keypress event. Secondly, the way to prevent the default action is to call preventDefault() on the event in non-IE browsers and set the event's returnValue property to false in IE.

var button = document.getElementById("button");
button.onkeypress = function(evt) {
   evt = evt || window.event;
   var charCode = evt.keyCode || evt.which;
   if (charCode == 32) {
       if (evt.preventDefault) {
           evt.preventDefault();
       } else {
           evt.returnValue = false;
       }
   }
};

I'm not a jQuery expert and I assume it takes care of obtaining the event for you:

$("button").keypress(function(evt) {
   var charCode = evt.keyCode || evt.which;
   if (charCode == 32) {
       if (evt.preventDefault) {
           evt.preventDefault();
       } else {
           evt.returnValue = false;
       }
   }
});
Tim Down
I tested it, and the `key.preventDefault();` changes nothing in firefox. `keydown` does detect keys, which produce printable characters, so whats wrong with `keydown`?
johannes
OK. What's the HTML that produces the button? Are you sure the keypress handler is being called? In the case of space, you're probably OK to use `keydown` and `keyCode` 32, but in general with printable characters using `keypress` abstracts away any potential difference between keyboards or other input devices by extracting the character that resulted from the keypress rather than a code corresponding to a key on an input device.
Tim Down
@Tim: the OPs original code sample is valid jQuery for cancelling the event. None of the usual cross-browser code switching is necessary in this case.
Crescent Fresh
@cresecentfresh: OK. Guess the fact I don't use jQuery is showing through. When someone posts a better answer I'll delete this.
Tim Down
A: 

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.

Tim Down