怎样判断文本框内的内容是否有效

[quary]

判断文本框的内容如果所有字符都是空格,是value即为空,怎么判断?

[meizz]

<input name=mm><input type=button value=ok onclick=cc()>

<script language=Javascript> //自己动手为string添加Trim
function String.prototype.Trim() {return this.replace(/(^\s*)|(\s*$)/g,"");}
function cc()
{
var e = document.all.mm;
if (e.value.Trim() == "")
{ alert("为空"); e.value="";}
else alert("不是空的");
}
</script>

[quary]

太好啦终于有Trim了,谢了