限制textarea字符长度

<script>
function checkLength(obj,maxlength){
    if(obj.value.length > maxlength){
        obj.value = obj.value.substring(0,maxlength);
    }
}
</script>

<textarea name="content" cols="" rows="8" onpropertychange="checkLength(this,140);" oninput="checkLength(this,140);"></textarea