Automatically expand text area

Question

I'm trying to make a simple auto-expanding text area. This is my code:

textarea.onkeyup = function () {
  textarea.style.height = textarea.clientHeight + 'px';
}

But the text area will grow infinitely as you type...

I know there are Dojo and jQuery plugins for this, but I don't want to use them. I looked at their implementation and originally used scrollHeight but did the same thing.

You can start answering and use the text area to play your answer.

Answer 1

I want the auto-expand area to be limited by the number of rows (e.g. 5 rows). I considered using "em" units, for Rob's solution, however, this is error-prone and doesn't take into account stuff like padding.

This is my idea:

var textarea = document.getElementById("textarea");
var limitRows = 5;
var messageLastScrollHeight = textarea.scrollHeight;

textarea.oninput = function() {
    var rows = parseInt(textarea.getAttribute("rows"));
    // If we don't decrease the amount of rows, the scrollHeight would show the scrollHeight for all the rows
    // even if there is no text.
    textarea.setAttribute("rows", "1");

    if (rows < limitRows && textarea.scrollHeight > messageLastScrollHeight) {
        rows++;
    } else if (rows > 1 && textarea.scrollHeight < messageLastScrollHeight) {
        rows--;
    }

    messageLastScrollHeight = textarea.scrollHeight;
    textarea.setAttribute("rows", rows);
};

Fiddle:http://jsfiddle.net/cgSj3/

Answer 2

Reset the height before correctly expanding/shrinking the text area using scrollHeight. Math.min() Can be used to set the height limit of the text area.

Code:

var textarea = document.getElementById("textarea");
var heightLimit = 200; /* Maximum height: 200px */

textarea.oninput = function() {
  textarea.style.height = ""; /* Reset the height*/
  textarea.style.height = Math.min(textarea.scrollHeight, heightLimit) + "px";
};

Fiddle: http://jsfiddle.net/gjqWy/155

Note: input events are not supported in IE8 and earlier. If you also want to support this ancient browser, please use keydown or keyup and onpaste and/or oncut.