将日期的最后一天设置为YYYYMM日期格式-Javascript

Question

我有一个变量，其日期值为YYYYMM格式。 例如：

     var givenDate = "201704"

我如何找出给定月份的最后一天并将其追加。 例如，

     //last day of 2017 04 (April) is 30th so append value to givenDate + lastDate; 
     //that will be 20170430
      var newFullGivenDate = "20170430";

Answer 1

 const date = "201704"; const year = parseInt(date.substring(0, 4)); const month= parseInt(date.substring(4, 6)); const lastDay = (new Date(year, month, 0)).getUTCDate(); const newFullGivenDate = date + lastDay; console.log(newFullGivenDate); 

Answer 2

 var givenDate = "201704"; var month = givenDate.substring(4, givenDate.length); // retrieves 04 var year = givenDate.substring(0, 4); // retrieves 2017 var d = new Date(year, month, 0); alert(d.getDate()); 

参考： MDN

Answer 3

为了达到预期的效果，请使用以下选项

一个月的最后一天-新日期（年，月，0）

var givenDate = "201704";
var currDate = new Date(givenDate.substr(0,3),givenDate.substr(4) ,0)
var newFullGivenDate = givenDate + currDate.getDate();
console.log(newFullGivenDate)

Codepen网址以供参考- https://codepen.io/nagasai/pen/OmgZMW

Answer 4

我将其分解为两个功能：

 // Get last day from year and month let lastDayOf = (year, month) => (new Date(year, month, 0)).getDate(); // Add last day to string only if input is correct let addLastDay = (input) => { // In case you pass number (201705) instead of string ("201705") if (Number.isInteger(input)) input = input.toString(); // Check if input is in correct format - 6 digit string if (typeof input !== "string" || !input.match(/^\\d{6}$/)) { return input; // You can implement desired behavour here. I just return what came } const year = input.substr(0, 4); const month = input.substr(4, 2); return input + lastDayOf(year, month); } // Tests console.assert(addLastDay("201704"), "20170430"); console.assert(addLastDay("201702"), "20170228"); console.assert(addLastDay("201202"), "20120229"); console.assert(addLastDay(201705), "20170531"); console.assert(addLastDay(20170), 20170); // Wrong input // Interactive example document.getElementsByTagName('button')[0].addEventListener('click', () => { let input = document.getElementsByTagName('input')[0]; input.value = addLastDay(input.value); }); 

 <input type="text" value="201704"><button>Calculate</button> 

Answer 5

如果您正在使用moment js，则可以这样：

var date = moment(newFullGivenDate ).format('YYYYMMDD');

date = date.add(-1 * parseInt(date.format('DD')), 'days').add(1, 'months');