Question

在美国，顿悟的基督徒节日发生在1月2日至1月8日（含）的星期日。我正在尝试使用Javascript来查找它所处的日期。看起来它应该可行，但我什么都没得到：

var startDate = new Date(2018,0,2);
var endDate = new Date(2018,0,8);
var epiphanyUS = new Date();

while (startDate < endDate){
  if (startdate.getDay() === 0){
    epiphanyUS = startdate;
  }
  startDate.setDate(startDate.getDate() + 1);
}
console.log("Epiphany is" + epiphanyUS.format("MM-DD-YYYY"));

Answer 1

我修复了你的几个拼写错误并明确定义了所有变量。我认为你的while循环逻辑也可以更清晰。我不知道你是否在使用外部JS库（时刻？），但.format并不是我熟悉的方法。最后，我添加了一个年变量，因此您可以快速修改它以在任何其他年份找到顿悟。

＆＃13;

var year = 2018;
var startDate = new Date(year,0,2);
var endDate = new Date(year,0,8);
var epiphanyUS;

while (startDate <= endDate) {
    if (startDate.getDay() === 0) {
        epiphanyUS = startDate;
        break;
    } else {
        startDate.setDate(startDate.getDate() + 1);
    }
}

console.log("Epiphany is " + epiphanyUS.toDateString());

＆＃13;

Answer 2

如果您更喜欢使用return语句，也可以将逻辑包装在函数中。

＆＃13;

var startDate = new Date(2018,0,2);
var endDate = new Date(2018,0,8);

function getEpiphanyUS (startDate, endDate) {

  while (startDate <= endDate) {
    if (startDate.getDay() === 0){
      return startDate
    }
    startDate.setDate(startDate.getDate() + 1);
  }

}

var epiphanyUS = getEpiphanyUS (startDate, endDate)
console.log("Epiphany is " + epiphanyUS.toDateString());

＆＃13;

Answer 3

找到匹配项时应使用break。它可以让你走出循环。

var startDate = new Date(2018,0,2);
var endDate = new Date(2018,0,8); 
var epiphanyUS; // you should also define the variable you intend to use later.
    
while (startDate <= endDate){ // inclusive of endDate
  if (startDate.getDay() === 0){
    epiphanyUS = startDate; // fix the typo. It's startDate, not startdate
    break; // break when match is found.
  }
  startDate.setDate(startDate.getDate() + 1);
}
// check for presence and do stuff accordingly, like console.log
if(epiphanyUS) console.log("Epiphany is " + epiphanyUS);

Answer 4

＆＃13;

var startDate = new Date(2018,0,2);
var endDate = new Date(2018,0,8);
var epiphanyUS;
    
while (startDate < endDate){
  if (startDate.getDay() === 0){
    epiphanyUS = startDate;
  }
  startDate.setDate(startDate.getDate() + 1);
}
function format(date) {
  var year = date.getFullYear();

  var month = (1 + date.getMonth()).toString();
  month = month.length > 1 ? month : '0' + month;

  var day = date.getDate().toString();
  day = day.length > 1 ? day : '0' + day;
  
  return month + '/' + day + '/' + year;
}
console.log("Epiphany is " + format(epiphanyUS));

＆＃13;

注意像startDate和startdate这样的大写拼写错误。

Answer 5

如果您减少逻辑以在特定年份的1月2日或之后返回第一个星期日，则可以大大简化代码：

＆＃13;

/* @param {number} year - year to get epiphany for. Defaults to current year
** @returns {Date} First Sunday on or after 2 January for given year
*/
function getEpiphanyUS(year = new Date().getFullYear()) {
  var d = new Date(year, 0, 2);
  d.setDate(d.getDate() + ((7 - d.getDay()) % 7));
  return d;
}

// Test 2018 + next 9 years
for (var i=0; i<10; i++) {
  console.log(getEpiphanyUS(2018 + i).toString());
}

＆＃13;

在Javascript中查找两个日期之间的星期日

5 个答案: