Textarea to resize based on content length

Use this function:

function adjustHeight(el){
    el.style.height = (el.scrollHeight > el.clientHeight) ? (el.scrollHeight)+"px" : "60px";
}

Use this html:

<textarea onkeyup="adjustHeight(this)"></textarea>

And finally use this css:

textarea {
min-height: 60px;
overflow-y: auto;
word-wrap:break-word
}

The solution simply is letting the scrollbar appears to detect that height needs to be adjusted, and whenever the scrollbar appears in your text area, it adjusts the height just as much as to hide the scrollbar again.

You may also try contenteditable attribute onto a normal p or div. Not really a textarea but it will auto-resize without script.

.divtext {
    border: ridge 2px;
    padding: 5px;
    width: 20em;
    min-height: 5em;
    overflow: auto;
}

<div class="divtext" contentEditable>Hello World</div>

You can check the content's height by setting to 1px and then reading the scrollHeight property:

function textAreaAdjust(element) {
  element.style.height = "1px";
  element.style.height = (25+element.scrollHeight)+"px";
}

<textarea onkeyup="textAreaAdjust(this)" style="overflow:hidden"></textarea>

It works under Firefox 3, IE 7, Safari, Opera and Chrome.