Posted in: Using jQuery Core

Selecting Elements

The most basic concept of jQuery is to "select some elements and do something with them." jQuery supports most CSS3 selectors, as well as some non-standard selectors. For a complete selector reference, visit the Selectors documentation on api.jquery.com.

link Selecting Elements by ID

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$( "#myId" ); // Note IDs must be unique per page.

link Selecting Elements by Class Name

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$( ".myClass" );

link Selecting Elements by Attribute

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$( "input[name='first_name']" ); // Beware, this can be very slow in older browsers

link Selecting Elements by Compound CSS Selector

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$( "#contents ul.people li" );

link Pseudo-Selectors

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$( "a.external:first" );
$( "tr:odd" );
// Select all input-like elements in a form (more on this below).
$( "#myForm :input" );
$( "div:visible" );
// All except the first three divs.
$( "div:gt(2)" );
// All currently animated divs.
$( "div:animated" );

Note: When using the :visible and :hidden pseudo-selectors, jQuery tests the actual visibility of the element, not its CSS visibility or display properties. jQuery looks to see if the element's physical height and width on the page are both greater than zero.

However, this test doesn't work with <tr> elements. In the case of <tr> jQuery does check the CSS display property, and considers an element hidden if its display property is set to none.

Elements that have not been added to the DOM will always be considered hidden, even if the CSS that would affect them would render them visible. See the Manipulating Elements section to learn how to create and add elements to the DOM.

link Choosing Selectors

Choosing good selectors is one way to improve JavaScript's performance. A little specificity – for example, including an element type when selecting elements by class name – can go a long way. On the other hand, too much specificity can be a bad thing. A selector such as #myTable thead tr th.special is overkill if a selector such as #myTable th.special will get the job done.

jQuery offers many attribute-based selectors, allowing selections based on the content of arbitrary attributes using simplified regular expressions.

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// Find all <a> elements whose rel attribute ends with "thinger".
$( "a[rel$='thinger']" );

While these can be useful in a pinch, they can also be extremely slow in older browsers. Wherever possible, make selections using IDs, class names, and tag names.

link Does My Selection Contain Any Elements?

Once you've made a selection, you'll often want to know whether you have anything to work with. A common mistake is to use:

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// Doesn't work!
if ( $( "div.foo" ) ) {
...
}

This won't work. When a selection is made using $(), an object is always returned, and objects always evaluate to true. Even if the selection doesn't contain any elements, the code inside the if statement will still run.

The best way to determine if there are any elements is to test the selection's .length property, which tells you how many elements were selected. If the answer is 0, the .length property will evaluate to false when used as a boolean value:

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// Testing whether a selection contains elements.
if ( $( "div.foo" ).length ) {
...
}

link Saving Selections

jQuery doesn't cache elements for you. If you've made a selection that you might need to make again, you should save the selection in a variable rather than making the selection repeatedly.

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var divs = $( "div" );

In the example above, the variable name begins with a dollar sign. Unlike in other languages, there's nothing special about the dollar sign in JavaScript – it's just another character. Here, it's used to indicate that the variable contains a jQuery object. This practice is merely convention, and is not mandatory.

Once the selection is stored in a variable, you can call jQuery methods on the variable just like you would have called them on the original selection.

A selection only fetches the elements that are on the page at the time the selection is made. If elements are added to the page later, you'll have to repeat the selection or otherwise add them to the selection stored in the variable. Stored selections don't magically update when the DOM changes.

link Refining & Filtering Selections

Sometimes the selection contains more than what you're after. jQuery offers several methods for refining and filtering selections.

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// Refining selections.
$( "div.foo" ).has( "p" ); // div.foo elements that contain <p> tags
$( "h1" ).not( ".bar" ); // h1 elements that don't have a class of bar
$( "ul li" ).filter( ".current" ); // unordered list items with class of current
$( "ul li" ).first(); // just the first unordered list item
$( "ul li" ).eq( 5 ); // the sixth

link Selecting Form Elements

jQuery offers several pseudo-selectors that help find elements in forms. These are especially helpful because it can be difficult to distinguish between form elements based on their state or type using standard CSS selectors.

link :button

Using the :button pseudo-selector targets any <button> elements and elements with a type="button":

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$( "form :button" );

In order to get the best performance using :button, it's best to first select elements with a standard jQuery selector, then use .filter( ":button" ). More can be seen on the jQuery :button documentation page. Another option is to precede the pseudo-selector with a tag name or some other selector.

link :checkbox

Using the :checkbox pseudo-selector targets any <input> elements with a type="checkbox":

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$( "form :checkbox" );

Much like the :button pseudo-selector, it's best to first select elements with a standard jQuery selector, then to use .filter( ":checkbox" ), or to precede the pseudo-selector with some other selector.

link :checked

Not to be confused with :checkbox, :checked targets checked checkboxes, but keep in mind that this selector works also for checked radio buttons, and select elements (for select elements only, use the :selected selector):

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$( "form :checked" );

The :checked pseudo-selector works when used with checkboxes, radio buttons and selects.

link :disabled

Using the :disabled pseudo-selector targets any <input> elements with the disabled attribute:

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$( "form :disabled" );

In order to get the best performance using :disabled, first select elements with a standard jQuery selector, then use .filter( ":disabled" ), or precede the pseudo-selector with a tag name or some other selector.

link :enabled

Basically the inverse of the :disabled pseudo-selector, the :enabled pseudo-selector targets any elements that do not have a disabled attribute:

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$( "form :enabled" );

In order to get the best performance using :enabled, first select elements with a standard jQuery selector, then use .filter( ":enabled" ), or precede the pseudo-selector with a tag name or some other selector.

link :file

Using the :file pseudo-selector targets any <input> elements that have a type="file":

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$( "form :file" );

In order to get the best performance using :file, first select elements with a standard jQuery selector, then use .filter( ":file" ), or precede the pseudo-selector with a tag name or some other selector.

Note: For better performance in modern browsers, use [type="file"] instead of the :file pseudo-selector.

link :image

Using the :image pseudo-selector targets any <input> elements that have a type="image":

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$( "form :image" );

In order to get the best performance using :image, first select elements with a standard jQuery selector, then use .filter( ":image" ), or precede the pseudo-selector with a tag name or some other selector.

Note: For better performance in modern browsers, use [type="image"] instead of the :image pseudo-selector.

link :input

Using the :input selector selects all <input>, <textarea>, <select>, and <button> elements:

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$( "form :input" );

link :password

Using the :password pseudo-selector targets any <input> elements with a type="password":

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$( "form :password" );

In order to get the best performance using :password, first select elements with a standard jQuery selector, then use .filter( ":password" ), or precede the pseudo-selector with a tag name or some other selector.

Note: For better performance in modern browsers, use [type="password"] instead of the :password pseudo-selector.

link :radio

Using the :radio pseudo-selector targets any <input> elements that have a type="radio":

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$( "form :radio" );

To select a set of associated radio buttons use:

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// Selects all radio buttons with the name attribute of gender.
$( "form input[name='gender']:radio" );

In order to get the best performance using :radio, first select elements with a standard jQuery selector, then use .filter( ":radio" ), or precede the pseudo-selector with a tag name or some other selector.

Note: For better performance in modern browsers, use [type="radio"] instead of the :radio pseudo-selector.

link :reset

Using the :reset pseudo-selector targets any <input> elements that have a type="reset":

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$( "form :reset" );

In order to get the best performance using :reset, first select elements with a standard jQuery selector, then use .filter( ":reset" ), or precede the pseudo-selector with a tag name or some other selector.

Note: For better performance in modern browsers, use [type="reset"] instead of the :reset pseudo-selector.

link :selected

Using the :selected pseudo-selector targets any selected items in <option> elements:

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$( "form :selected" );

In order to get the best performance using :selected, first select elements with a standard jQuery selector, then use .filter( ":selected" ), or precede the pseudo-selector with a tag name or some other selector.

link :submit

Using the :submit pseudo-selector targets any <button> or <input> elements with a type="submit":

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$( "form :submit" );

The :submit selector usually applies to <button> or <input> elements. Some browsers (such as Internet Explorer) do not automatically give the <button> element a type="submit" by default.

Note: For better performance in modern browsers, use [type="submit"] instead of the :submit pseudo-selector.

link :text

Using the :text pseudo-selector targets any <input> elements with a type="text":

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$( "form :text" );

In order to get the best performance using :text, first select elements with a standard jQuery selector, then use .filter( ":text" ), or precede the pseudo-selector with a tag name or some other selector.

Note: As of jQuery 1.5.2, :text selects <input> elements that have no specified type attribute. So, type="text" is implied.