How to determine where focus went?

This has been asked here before, but several years ago, and there was no cross-platform solution at the time (other than the setTimeout solution, which is really not very handy).

I'd like to do onblur="foo(parm);" and have foo be able to determine which element now has focus.

I'm using regular javascript; no jQuery for this one, please.

Is that possible these days?

回答1:

You can try something like this:

function whereDidYouGo() {
    var all = document.getElementsByTagName('*');

        for (var i = 0; i < all.length; i++)
            if (all[i] === all[i].ownerDocument.activeElement)
                return all[i];
}

EDIT:

function whereDidYouGo() { return document.activeElement; }

回答2:

In jQuery, at the OP's request:

$(':input').blur(function() {
    $focusedElement = $(':input:focus');
    //Do stuff with $focusedElement
}

回答3:

Interesting question. The heart of the matter is - when does the 'focus' event fire, before or after the blur event? If it fires before the blur event, the problem is easy, because you can just store the current focus in a variable that your blur event can access.

However, at least in Chrome 13, it appears the blur event happens before the focus event. One possible solution.

Given the following HTML:

<input id="foo" value='foo' />
<input id="bar" value='bar' />

You can then:

var currentFocus;
var pendingBlur;

var foo = document.getElementById('foo');
foo.addEventListener('focus', function(){ 
    currentFocus = foo;
    if(pendingBlur !== undefined){
        pendingBlur();
        pendingBlur = undefined;
    }
});
foo.addEventListener('blur', function(){
    pendingBlur = function(){
        console.log('new focus:', currentFocus);
    };
});

var bar= document.getElementById('bar');
bar.addEventListener('focus', function(){ 
   currentFocus = bar;
   if(pendingBlur !== undefined){
        pendingBlur();
        pendingBlur = undefined;
   }
});
bar.addEventListener('blur', function(){
    pendingBlur = function(){
        console.log('new focus:', currentFocus);
    };
});

Basically, I just not the blur callback so it is handy for the focus event to call after we know about which element was focused.

Here is a working example on JSFiddle.

EDIT: This solution suffers from the problem that if you blur on the form by clicking on something other than another form element, the blur event never fires (since we wait for the focus event). The only way around that, that I can conceive, is using a timer to check if pendingBlur is defined, and if so, call it. At which point you don't really need the focus event to call the blur callback anymore...