Make input element (type="text") handle multiple lines of text

I've created a form with an input, but the box only handles text in a single row. I would like to style it so that the input field is similar to that of Twitter's, where the box itself is multiple rows:

And it also expands when you hit enter:

This is currently what I have:

<form name="userForm">
  <input type="text" id="userInput" name="userInput" placeholder="Enter text here.">
  <button type="submit" id="button">Submit</button>
</form>

I've styled the button and the input, but haven't done anything to change its shape, so it's at default. What do I have to tweak to achieve this?

Solution

You need to use an HTML <textarea> element.

From MDN:

<textarea>

The HTML <textarea> element represents a multi-line plain-text editing control.

Using <input> for multiline text is not possible natively and, if hacked, would be invalid HTML.

HTML5 spec:

4.10.5.1.2 Text (type=text) state and Search state (type=search)

The input element represents a one line plain text edit control for the element's value.

(emphasis mine)

Twitter input box

You mention you want the textarea to resemble Twitter's (auto-resize / no scrollbar). Consider this option and the following SO posts:

Autosize

A small, stand-alone script to automatically adjust textarea height.