textarea中输入字数的限制

<textarea id="area" name="ss" placeholder="请输入文本内容"  rows="10" cols="50" onkeydown=‘inputLimit(this,1,2000);‘ onkeyup=‘inputLimit(this,1,2000);‘></textarea>
<script type="text/javascript">
    /*字数限制*/
function inputLimit(field, type, maxlimit) {
	if (type == 1) {
		if (field.value.replace(/[^\x00-\xff]/g, "xx").length > maxlimit) {
			alert("输入字数已达上项");
			var str = "";
			var n = 0;
			var schar;
			for (var i = 0; schar = field.value.charAt(i); i++) {
				n += (schar.match(/[^\x00-\xff]/) != null ? 2 : 1);
				if (n > maxlimit)
					break;
				str += schar;
			}
			field.value = str;
		}
	}
}
</script>