动态获取特定工作日最后一次出现的日期 [英] Get date of last occurrence of a specific weekday dynamically

问题描述

我正在尝试创建一个函数，该函数返回特定工作日的日期，即上次发生的时间.

I'm trying to create a function that returns the date of a specific weekday, the last time it occurred.

例如，今天是2016年8月16日，星期二.如果我正在寻找上周五，它将返回2016-08-12.

For example, today it's Tuesday, 2016-08-16. If I was looking for last Friday, it should return 2016-08-12.

当前，我使用的代码是为特定工作日编写的.我该如何更改它以使其返回我要求的工作日的日期?

Currently, the code I'm using is written for a specific weekday. How could I change this to make it return the date of whatever weekday I'm asking for?

let t = new Date().getDate() + (6 - new Date().getDay() - 1) - 7;
let d = new Date();
d.setDate(t);

推荐答案

var WEEK_DAYS = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
var MILLIS_PER_DAY = 86400000;

function lastOccurrenceOf(weekDay) {
  var desiredIndex = WEEK_DAYS.indexOf(weekDay);
  var currentDate = new Date;
  var daysDifference = (currentDate.getDay() - desiredIndex + 6) % 7 + 1; //the number of days ago
  return new Date(currentDate.getTime() - MILLIS_PER_DAY * daysDifference);
}
console.log(lastOccurrenceOf('Tuesday').toString());
console.log(lastOccurrenceOf('Friday').toString());

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