The .before() and .insertBefore() methods perform the same task. The major difference is in the syntax-specifically, in the placement of the content and target. With .before(), the selector expression preceding the method is the container before which the content is inserted. With .insertBefore(), on the other hand, the content precedes the method, either as a selector expression or as markup created on the fly, and it is inserted before the target container.

Consider the following HTML:

<div class="container">
  <h2>Greetings</h2>
  <div class="inner">Hello</div>
  <div class="inner">Goodbye</div>
</div>

You can create content and insert it before several elements at once:

$('.inner').before('<p>Test</p>');

Each inner <div> element gets this new content:

<div class="container">
  <h2>Greetings</h2>
  <p>Test</p>
  <div class="inner">Hello</div>
  <p>Test</p>
  <div class="inner">Goodbye</div>
</div>

You can also select an element on the page and insert it before another:

$('.container').before($('h2'));

If an element selected this way is inserted elsewhere, it will be moved before the target (not cloned):

<h2>Greetings</h2>
<div class="container">
  <div class="inner">Hello</div>
  <div class="inner">Goodbye</div>
</div>

If there is more than one target element, however, cloned copies of the inserted element will be created for each target after the first.

In jQuery 1.4, .before() and .after() will also work on disconnected DOM nodes:

$("<div/>").before("<p></p>");

The result is a jQuery set that contains a paragraph and a div (in that order).

Additional Arguments

Similar to other content-adding methods such as .prepend() and .after(), .before() also supports passing in multiple arguments as input. Supported input includes DOM elements, jQuery objects, HTML strings, and arrays of DOM elements.

For example, the following will insert two new <div>s and an existing <div> before the first paragraph:

var $newdiv1 = $('<div id="object1"/>'),
    newdiv2 = document.createElement('div'),
    existingdiv1 = document.getElementById('foo');

$('p').first().before($newdiv1, [newdiv2, existingdiv1]);

Since .before() can accept any number of additional arguments, the same result can be achieved by passing in the three <div>s as three separate arguments, like so: $('p').first().before($newdiv1, newdiv2, existingdiv1). The type and number of arguments will largely depend on how you collect the elements in your code.