Using jQuery to test if an input has focus

问题

On the front page of a site I am building, several <div>s use the CSS :hover pseudo-class to add a border when the mouse is over them. One of the <div>s contains a <form> which, using jQuery, will keep the border if an input within it has focus. This works perfectly except that IE6 does not support :hover on any elements other than <a>s. So, for this browser only we are using jQuery to mimic CSS :hover using the $(#element).hover() method. The only problem is, now that jQuery handles both the form focus() and hover(), when an input has focus then the user moves the mouse in and out, the border goes away.

I was thinking we could use some kind of conditional to stop this behavior. For instance, if we tested on mouse out if any of the inputs had focus, we could stop the border from going away. AFAIK, there is no :focus selector in jQuery, so I\'m not sure how to make this happen. Any ideas?

回答1:

jQuery 1.6+

jQuery added a :focus selector so we no longer need to add it ourselves. Just use $("..").is(":focus")

jQuery 1.5 and below

Edit: As times change, we find better methods for testing focus, the new favorite is this gist from Ben Alman:

jQuery.expr[':'].focus = function( elem ) {
  return elem === document.activeElement && ( elem.type || elem.href );
};

Quoted from Mathias Bynens here:

Note that the (elem.type || elem.href) test was added to filter out false positives like body. This way, we make sure to filter out all elements except form controls and hyperlinks.

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

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

or:

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

Any jQuery

If you just want to figure out which element has focus, you can use

$(document.activeElement)

If you aren't sure if the version will be 1.6 or lower, you can add the :focus selector if it is missing:

(function ( $ ) {
    var filters = $.expr[":"];
    if ( !filters.focus ) { 
        filters.focus = function( elem ) {
           return elem === document.activeElement && ( elem.type || elem.href );
        };
    }
})( jQuery );

回答2:

CSS:

.focus {
    border-color:red;
}

JQuery:

  $(document).ready(function() {

    $('input').blur(function() {
        $('input').removeClass("focus");
      })
      .focus(function() {
        $(this).addClass("focus")
      });
  });

回答3:

Here’s a more robust answer than the currently accepted one:

jQuery.expr[':'].focus = function(elem) {
  return elem === document.activeElement && (elem.type || elem.href);
};

Note that the (elem.type || elem.href) test was added to filter out false positives like body. This way, we make sure to filter out all elements except form controls and hyperlinks.

(Taken from this gist by Ben Alman.)

回答4:

April 2015 Update

Since this question has been around a while, and some new conventions have come into play, I feel that I should mention the .live method has been depreciated.

In its place, the .on method has now been introduced.

Their documentation is quite useful in explaining how it works;

The .on() method attaches event handlers to the currently selected set of elements in the jQuery object. As of jQuery 1.7, the .on() method provides all functionality required for attaching event handlers. For help in converting from older jQuery event methods, see .bind(), .delegate(), and .live().

So, in order for you to target the 'input focused' event, you can use this in a script. Something like:

$('input').on("focus", function(){
   //do some stuff
});

This is quite robust and even allows you to use the TAB key as well.

回答5:

I'm not entirely sure what you're after but this sounds like it can be achieved by storing the state of the input elements (or the div?) as a variable:

$('div').each(function(){

    var childInputHasFocus = false;

    $(this).hover(function(){
        if (childInputHasFocus) {
            // do something
        } else { }
    }, function() {
        if (childInputHasFocus) {
            // do something
        } else { }
    });

    $('input', this)
        .focus(function(){
            childInputHasFocus = true;
        })
        .blur(function(){
            childInputHasFocus = false;
        });
});

回答6:

An alternative to using classes to mark the state of an element is the internal data store functionality.

P.S.: You are able to store booleans and whatever you desire using the data() function. It's not just about strings :)

$("...").mouseover(function ()
{
    // store state on element
}).mouseout(function ()
{
    // remove stored state on element
});

And then it's just a matter of accessing the state of elements.

回答7:

if anyone cares there is a much better way to capture focus now, $(foo).focus(...)

http://api.jquery.com/focus/

回答8:

Have you thought about using mouseOver and mouseOut to simulate this. Also look into mouseEnter and mouseLeave

回答9:

Keep track of both states (hovered, focused) as true/false flags, and whenever one changes, run a function that removes border if both are false, otherwise shows border.

So: onfocus sets focused = true, onblur sets focused = false. onmouseover sets hovered = true, onmouseout sets hovered = false. After each of these events run a function that adds/removes border.

回答10:

As far as I know, you can't ask the browser if any input on the screen has focus, you have to set up some sort of focus tracking.

I usually have a variable called "noFocus" and set it to true. Then I add a focus event to all inputs that makes noFocus false. Then I add a blur event to all inputs that set noFocus back to true.

I have a MooTools class that handles this quite easily, I'm sure you could create a jquery plugin to do the same.

Once that's created, you could do check noFocus before doing any border swapping.

回答11:

There is no :focus, but there is :selected http://docs.jquery.com/Selectors/selected

but if you want to change how things look based on what is selected you should probably be working with the blur events.

http://docs.jquery.com/Events/blur

回答12:

There is a plugin to check if an element is focused: http://plugins.jquery.com/project/focused

$('input').each(function(){
   if ($(this) == $.focused()) {
      $(this).addClass('focused');
   }
})

回答13:

I had a .live("focus") event set to select() (highlight) the contents of a text input so that the user wouldn't have to select it before typing a new value.

$(formObj).select();

Because of quirks between different browsers, the select would sometimes be superseded by the click that caused it, and it would deselect the contents right after in favor of placing the cursor within the text field (worked mostly ok in FF but failed in IE)

I thought I could solve this by putting a slight delay on the select...

setTimeout(function(){$(formObj).select();},200);

This worked fine and the select would persist, but a funny problem arose.. If you tabbed from one field to the next, the focus would switch to the next field before the select took place. Since select steals focus, the focus would then go back and trigger a new "focus" event. This ended up in a cascade of input selects dancing all over the screen.

A workable solution would be to check that the field still has focus before executing the select(), but as mentioned, there's no simple way to check... I ended up just dispensing with the whole auto highlight, rather than turning what should be a single jQuery select() call into a huge function laden with subroutines...

回答14:

What I wound up doing is creating an arbitrary class called .elementhasfocus which is added and removed within the jQuery focus() function. When the hover() function runs on mouse out, it checks for .elementhasfocus:

if(!$("#quotebox").is(".boxhasfocus")) $(this).removeClass("box_border");

So if it doesn't have that class (read: no elements within the div have focus) the border is removed. Otherwise, nothing happens.

回答15:

Simple

 <input type="text" /> 



 <script>
     $("input").focusin(function() {

    alert("I am in Focus");

     });
 </script>

来源：https://stackoverflow.com/questions/967096/using-jquery-to-test-if-an-input-has-focus