JS　计算两日期时间相差多少天

function getDays(DateOne,DateTwo){
var OneMonth = DateOne.substring(5,DateOne.lastIndexOf ('-'));
var OneDay = DateOne.substring(DateOne.length,DateOne.lastIndexOf ('-')+1);
var OneYear = DateOne.substring(0,DateOne.indexOf ('-'));

var TwoMonth = DateTwo.substring(5,DateTwo.lastIndexOf ('-'));
var TwoDay = DateTwo.substring(DateTwo.length,DateTwo.lastIndexOf ('-')+1);
var TwoYear = DateTwo.substring(0,DateTwo.indexOf ('-'));

var cha=((Date.parse(OneMonth+'/'+OneDay+'/'+OneYear)- Date.parse(TwoMonth+'/'+TwoDay+'/'+TwoYear))/86400000);
return Math.abs(cha);
}