传统的表单控件textarea元素中属性maxlength 的示例是什么？

<input id="btn1" type="button" value="0">
<input id="btn2" type="button" value="1">
<input id="btn3" type="button" value="6">
<input id="btn4" type="button" value="默认">
<textarea id="test"></textarea>    
<script>
btn1.onclick = function(){
    test.setAttribute('maxlength','0');
};
btn2.onclick = function(){
    test.setAttribute('maxlength','1');
};    
btn3.onclick = function(){
    test.setAttribute('maxlength','6');
};
btn4.onclick = function(){
    test.removeAttribute('maxlength');
};
</script>