autogrow.js is a jQuery plugin that, like most plug-ins, was built out of frustration for lack of support for a much-needed feature, namely the ability for a textarea to automatically grow and shrink dynamically with its content. I received a head-start from this post, but decided I needed more functionality. It handles the paste event and 'ctrl+x', or cutting.

Basic usage (Interactive Demo):

$('textarea').autogrow(); //or some selector that will grab textareas

autogrow.js has some options that you can set:

• context: defaults to $(document). The parent element events will be delegated to. If you want to simply use defaults but want to pass in a context, you can just do that like this: $('textarea').autogrow($('.myContext'));
• animate: defaults to true. Set to false if you don't want the resizing of the box to be animated.
• speed: defaults to 200. Speed of the resize animation.
• fixMinHeight: defaults to true. Set to false if you don't want the box to stop shrinking when it hits its initial size.
• cloneClass: defaults to 'autogrowclone'. Helper CSS class for the clone used for measuring sizes. Use this if you need to apply special rules for a textbox that is right next to the one you're autogrowing, but not exactly it so that they are identical.
• onInitialize: defaults to false. Will trigger autogrow on init.

Example:

var opts = {
    context: $('li')
    , animate: false
    , cloneClass: 'faketextarea'
};
$('.mytextareas').autogrow(opts);