备注字段长度控制JS

		//变更原因备注字符长度控制
		function checkChangeLength() { 
			var field = $("#changeReasonDesc").val();
		    maxlimit=250; 
		    if (field.length > maxlimit){
		  		field = field.substring(0, maxlimit); 
		  		$.messager.alert("操作提示","最多只能输入250个汉字！","info");
		  		$("#projectDesc").val(field);
		    } 
	   }

<textarea id="changeReasonDesc" name="changeReasonDesc" style="760px;height:60px;font:12px/150% Arial,Verdana,'宋体';" placeholder="最多输入250个汉字" onkeyup="checkchangeLength();"></textarea>