Is there a 'has focus' in JavaScript (or j

问题:

Is there something I can do like this (perhap via a plugin)

if ( ! $('form#contact input]').hasFocus()) {
  $('form#contact input:first]').focus();
}

Basically, set focus to the first input, but only if the user has not already clicked into anything?

I know this will work too, but is there anything more elegant?

$(function() {
  var focused = false;
  $('form#contact input]').focus(function() {
    focused = true;
  }); 
  setTimeout(function() {
    if ( ! focused) {      
      $('form#contact input:first]').focus();
    }
  }, 500);
});

回答1:

There is no native solution but yes there is a more elegant way you can do it:

jQuery.extend(jQuery.expr[':'], {
  focus: "a == document.activeElement"
});

You're defining a new selector. See Plugins/Authoring. Then you can do:

if ($("...").is(":focus")) {
  ...
}

or:

$("input:focus").doStuff();

回答2:

$('input:focus')

It's CSS. You don't need to create a "custom selector." It already exists! http://www.w3schools.com/CSS/pr_pseudo_focus.asp

Just attach whatever process you want to do to that selector, and it will weed it out if the element in question is not focused. I did this recently to keep a keyup from instantiating an email input error check when the e-mail input wasn't being used.

If all you're trying to do is check if the user has focused on anything themselves, just do this:

if($('input:focus').size() == 0){
    /* Perform your function! */
}

回答3:

jQuery 1.6 now has a dedicated :focus selector.

回答4:

I had trouble with cletus approach, using jQuery 1.3.2 and Firefox 3.6.8, because the string "a == document.activeElement" was not a valid function.

I fixed it defining a function for the focus key. In fact, all other keys defined in jQuery.expr[':'] are defined as functions. Here's the code:

jQuery.extend(jQuery.expr[':'], {
    focus: function(e){ return e == document.activeElement; }
});

So, now it works as expected.

However, I was experiencing some strange behaviour in Firefox 3.6.8 (maybe a bug in FF?). If I clicked on an input text while the page was rendering, and if I called is(":focus") on page load, I would get an error from the browser, reported by FireBug, and the script would break.

To solve this, I surrounded the code with a try...catch block, returning false on error. Use it if you want to prevent your users from experiencing the same error:

jQuery.extend(jQuery.expr[':'], {
    focus: function(e){
        try{ return e == document.activeElement; }
        catch(err){ return false; }
    }
});

回答5:

No, there isn't.

However, you can simulate it like this:

$(':input')
    .data('focused', false)
    .focus(function() { $.data(this, 'focused', true); })
    .blur(function() { $.data(this, 'focused', false); });

回答6:

Frustratingly difficult to find a solution to this problem considering the solution is actually very simple:

if (document.activeElement == this) {
  // has focus
}

if (document.activeElement != this) {
  // does not have focus
}

回答7:

There is a plugin http://plugins.jquery.com/project/focused

Also you can check Using jQuery to test if an input has focus

回答8:

I know this is an old question, but may be my solution will help someone :)

since this didnt worked for me:

if ($(this)!=$(document.activeElement)) { ... }

..were "this" is returned from blur function. So i did this:

if ($(document.activeElement).attr("class") != "input_textbox"){ ... }

回答9:

Here is a succinct way to do it.

$(document.activeElement)

or to plug it into your example..

if ($('form#contact input]')[0]!=$(document.activeElement)) { ... }

回答10:

    $('*:focus')

(Necro ftw, but still valid and useful)