将onchange更改为“change”,并且您的日期不来自事件变量,您需要像这样“手动”获取它:
"use strict";
let nowDate = new Date();
let today = new Date(nowDate.getFullYear(), nowDate.getMonth(), nowDate.getDate(), 0, 0, 0, 0);
let enddate;
$('#startdatepicker').datepicker({
autoclose:true,
todayHighlight: true,
startDate:today
}).on("change",function(e){
var fromDate = $('#startdatepicker').val().split("/");
let present=new Date(fromDate[2] , fromDate[1] - 1 , fromDate[0]);
enddate = new Date(present.getFullYear(), present.getMonth(), present.getDate() + 1, 0, 0, 0, 0);
alert(enddate);
$('#enddatepicker').datepicker('setStartDate', enddate );
});