Javascript – Using jQuery to test if an input has focus

javascriptjqueryjquery-eventsjquery-on

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?

Best Answer

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 );

Related Solutions

Javascript – n “exists” function for jQuery

In JavaScript, everything is 'truthy' or 'falsy', and for numbers 0 means false, everything else true. So you could write:

if ($(selector).length)

You don't need that >0 part.

Javascript – Add table row in jQuery

The approach you suggest is not guaranteed to give you the result you're looking for - what if you had a tbody for example:

<table id="myTable">
  <tbody>
    <tr>...</tr>
    <tr>...</tr>
  </tbody>
</table>

You would end up with the following:

<table id="myTable">
  <tbody>
    <tr>...</tr>
    <tr>...</tr>
  </tbody>
  <tr>...</tr>
</table>

I would therefore recommend this approach instead:

$('#myTable tr:last').after('<tr>...</tr><tr>...</tr>');

You can include anything within the after() method as long as it's valid HTML, including multiple rows as per the example above.

Update: Revisiting this answer following recent activity with this question. eyelidlessness makes a good comment that there will always be a tbody in the DOM; this is true, but only if there is at least one row. If you have no rows, there will be no tbody unless you have specified one yourself.

DaRKoN_ suggests appending to the tbody rather than adding content after the last tr. This gets around the issue of having no rows, but still isn't bulletproof as you could theoretically have multiple tbody elements and the row would get added to each of them.

Weighing everything up, I'm not sure there is a single one-line solution that accounts for every single possible scenario. You will need to make sure the jQuery code tallies with your markup.

I think the safest solution is probably to ensure your table always includes at least one tbody in your markup, even if it has no rows. On this basis, you can use the following which will work however many rows you have (and also account for multiple tbody elements):

$('#myTable > tbody:last-child').append('<tr>...</tr><tr>...</tr>');