Can someone explain what = $(); means in jQuery?

Question

I have the following in some code I am looking at:

    // Save an empty jQuery in our cache for now.
    dialogs[id] = $();

Can anyone explain what it means. I have no idea about this concept. thanks

Update:

Here's a bit more of the code:

    var loadAndShowDialog = function (id, link, url) {
    var separator = url.indexOf('?') >= 0 ? '&' : '?';

    // Save an empty jQuery in our cache for now.
    dialogs[id] = $();

    // Load the dialog with the content=1 QueryString in order to get a PartialView
    $.get(url + separator + 'content=1')
        .done(function (content) {
            dialogs[id] = $('<div class="modal-popup">' + content + '</div>')
                .hide() // Hide the dialog for now so we prevent flicker
                .appendTo(document.body)
                .filter('div') // Filter for the div tag only, script tags could surface
                .dialog({ // Create the jQuery UI dialog
                    title: link.data('dialog-title'),
                    modal: true,
                    resizable: true,
                    draggable: true,
                    width: link.data('dialog-width') || 300
                })
                .find('form') // Attach logic on forms
                    .submit(formSubmitHandler)
                .end();
        });
};

I still cannot see the point of the first line. It's been explained to me that it creates an empty jquery object but I can't understand why.

Of course I can see the comment and you might know what it means but the reason for asking my question was that I do not know what it means. Please understand one of the purposes of this site is to help people. — Samantha J T Star, Feb 02 '12 at 06:19

score 3 · Answer 1 · answered Feb 02 '12 at 06:11

3

It creates an empty jQuery object. This object contains no actual elements, but it does have all the jQuery functionality added to it.

var $el = $();
// later you can do…
$el = $el.add('body'); // same effect as if you’d written `$el = $('body');`

answered Feb 02 '12 at 06:11

Mathias Bynens

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score 2 · Answer 2 · answered Feb 02 '12 at 06:14

2

From the docs (you did check the docs, right?):

Returning an Empty Set

As of jQuery 1.4, calling the jQuery() method with no arguments returns an empty jQuery set (with a .length property of 0).

answered Feb 02 '12 at 06:14

Jordan Running

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Thanks for your explanation but what would be the point of doing this? – Samantha J T Star Feb 02 '12 at 06:21
@SamanthaJ - it's like initializing an array to `[]`. It's an empty object, ready to have things added to it. – jfriend00 Feb 02 '12 at 06:28
@jfriend00 - Thanks. Did you see the code I added. I wonder if this initialization is really needed in this example. – Samantha J T Star Feb 02 '12 at 07:15

Richard Neil Ilagan · Accepted Answer · 2012-02-02T07:53:59.147

The other answers are correct; calling $() creates an empty jQuery object.

In the context of your existing code, though, it seems that it's not needed. The dialogs[id] variable, which was initialized with $() is only reassigned with another value, without using its original value.

One thing to take note of, however, is that the dialogs[id] variable is subsequently given another value during the completion of an AJAX call, which means that it may be used somewhere else in your code while the asynchronous operation $.get is going on. It may be inside a function, but it's not properly scoped using var, so that's a bit dubious.

From what it looks like (and based on how its used) though, I'm willing to bet that it's not, and you may be correct that the $() initialization is completely unnecessary.

Can someone explain what = $(); means in jQuery?

3 Answers3

Returning an Empty Set

Linked