不管今天是星期几使用JavaScript，如何在9周前找到星期日

如何解决不管今天是星期几使用JavaScript，如何在9周前找到星期日

希望有人可以帮助我。我试图编写一个函数来查找9周前的星期日，而不管今天的星期几使用javascript。
我尝试使用moment（）。day（-56），但无法正常工作。还有其他方法可以做到这一点吗？

解决方法

这是您要找的吗？

console.log(moment().startOf('week').subtract(9,'weeks').format("MM-DD-yyyy"))

星期天是一周的开始，因此我们去那里寻找基准。然后，使用Momentjs减去函数从那里减去9周。格式化以方便输出。

根据https://momentjscom.readthedocs.io/en/latest/moment/02-get-set/06-day/，您可以在9个星期日之前获得：

import scss from "rollup-plugin-scss";

export default {
  input: "./src/scripts/main.js",output: {
    file: "./build/js/main.min.js",format: "esm",},plugins: [
    scss({
      output: "./build/css/style.css",failOnError: true,runtime: require("sass"),}),],};

我认为您需要分别计算星期和工作日。试试这样的事情：https://codepen.io/kevinashworth/pen/bGeGjGx

var thisWeek = moment().week()
var theSunday = moment().week(thisWeek - 9).weekday(0).format("dddd,MMMM Do,YYYY")

我假设您需要在9周前找到第一个星期日，所以也许波纹管功能会有所帮助。

const findNineWeeksAgo = () => {
  let nineWeeksAgo = new Date('August 19,1975 23:15:30')
  const nineWeeksInDays = 63

  // You can modify a date using setDate. It automatically corrects for shifting to new months/years etc.
  nineWeeksAgo.setDate(nineWeeksAgo.getDate() - nineWeeksInDays);

  return nineWeeksAgo
}

const findNextSunday = () => {
  const dateNineWeeksAgo = findNineWeeksAgo()
  // getting the exact day of the week that was 9 weeks ago
  let dayNineWeeksAgoe = dateNineWeeksAgo.getDay()
  // if the exact day is sunday i.e 0 return that date in string format else find number of days to sunday add them to the exact date and reurn that.
  if (dayNineWeeksAgoe === 0) return dayNineWeeksAgoe.toString()
  else {
    let daysLeftToSunday = 7 - dayNineWeeksAgoe
    dateNineWeeksAgo.setDate(dateNineWeeksAgo.getDate() + daysLeftToSunday);
    return dateNineWeeksAgo.toString()
  }
}

console.log(findNextSunday())

如果您选择仅使用本机JS，这可能适合您的需求。

<script>
 var today = new Date();
 // today.getDay() is current day-of-week (0=Sun ... 6=Sat)
 var lastSun9wksAgo = new Date(today.getFullYear(),today.getMonth(),today.getDate()-(9*7+today.getDay()));
 // alter display for 9 weeks ago with day-of-week offset
 alert(lastSun9wksAgo.toDateString());
</script>

如果重复使用，可以放在两行函数中，例如：

    <script>
function sundayPriorWeeks(weeks) {
  var today = new Date();
  // today.getDay() is current day-of-week (0=Sun ... 6=Sat)
  var lastSun9wksAgo = new Date(today.getFullYear(),today.getDate()-(9*7+today.getDay()));
  // alter display for # weeks ago with day-of-week offset
  return lastSun9wksAgo;
}
alert(sundayPriorWeeks(9).toDateString());
</script>