jquery时间加法

<td style="width:150px">
    <input name="startDate" id="startDate" class="cword" onClick="WdatePicker({skin:'whyGreen',dateFmt:'yyyy-MM-dd HH:mm:ss'})" onclick="addDate();"/>
</td>
<td style="width:150px">
	<input name="endDate" id="endDate" class="cword" 
onClick="WdatePicker({skin:'whyGreen',dateFmt:'yyyy-MM-dd HH:mm:ss'})" />
</td>

页面显示如上：

页面js处理如下：

function addDate(){
		var startDate = $("#startDate").val();
		if(startDate == null || startDate == ""){
			$("#endDate").val("");
			return false;
		}
		var sd = new Date(startDate.replace(/-/g,"/")).getTime();
		var examLength = 0;
		if('${examClassPaper.examLength}' != null &&     '${examClassPaper.examLength}' != ''){
		examLength = '${examClassPaper.examLength}';
		}else{
				examLength = 1;
		}
		var endDate = sd + examLength*60*1000;
		var newDate = new Date();
		newDate.setTime(endDate);
		endDate = newDate.format("yyyy-MM-dd hh:mm:ss");
		$("#endDate").val(endDate);
		//alert(endDate);
	}

　相应的需要对应的format函数

Date.prototype.format = function(format) {
	      var date = {
	              "M+": this.getMonth() + 1,
	              "d+": this.getDate(),
	              "h+": this.getHours(),
	              "m+": this.getMinutes(),
	              "s+": this.getSeconds(),
	              "q+": Math.floor((this.getMonth() + 3) / 3),
	              "S+": this.getMilliseconds()
	       };
	       if (/(y+)/i.test(format)) {
	              format = format.replace(RegExp.$1, (this.getFullYear() + '').substr(4 - RegExp.$1.length));
	       }
	       for (var k in date) {
	              if (new RegExp("(" + k + ")").test(format)) {
	                     format = format.replace(RegExp.$1, RegExp.$1.length == 1
	                            ? date[k] : ("00" + date[k]).substr(("" + date[k]).length));
	              }
	       }
	       return format;
	}