An expanding text area is a multi-line text input field that expands in height to fit its contents. Commonly found in both desktop and mobile applications, such as the SMS composition field on the iPhone, it’s a good choice when you don’t know how much text the user will write and you want to keep the layout compact; as such, it’s especially useful on interfaces targeted at smartphones. Yet despite the ubiquity of this control, there’s no way to create it using only HTML and CSS, and most JavaScript solutions have suffered from guesswork, inaccuracy, or a lack of elegance … until now.