[textarea] To increase the height automatically

[HTML]

<textarea class="test" onkeyup="this.style.height='26px'; this.style.height = this.scrollHeight + 'px';"></textarea>

[CSS]

.test {

    resize:none;

    line-height:30px;

    width:100%;

    overflow-y:hidden;

    height:30px;

}

thank!