具有多个变量的 IF 语句

Question

我有一个倒计时应用程序运行宁多个日期。我想运行 clearInterval()，当每个到达日期并停止时钟时。

我有我当前的日期和存储的日期：

const currentDate = new Date()

const stageOneA = new Date ('March 8, 2021 00:00:00'),
stageOneB = new Date('March 29,2021 00:00:00'),
stageTwo = new Date('April 12, 2021 00:00:00'),
stageThree = new Date('March 3,2021 00:00:00'),
stageFour = new Date('June 21,2021 00:00:00').getTime()

然后我想写一个IF语句来检查currentDate是否小于或等于每个日期，然后调用clearInterval。这适用于一个变量，但不适用于所有变量。

我认为下面的方法行得通，但行不通。我哪里错了？

if(stageOneA || stageOneB || stageTwo || stageThree || stageFour <= currentDate) {
    clearInterval(updateCountdown)
 }

Answer 1

这是一个很常见的错误，它是有道理的。

正确的代码可能是最好的解释方式：

if (stageOneA <= currentDate ||
    stageOneB <= currentDate ||
    stageTwo <= currentDate ||
    stageThree <= currentDate ||
    stageFour <= currentDate) 
{

    clearInterval(updateCountdown);
}

您必须单独检查每个阶段。

您的原始代码是说检查前 4 个日期是否存在，然后检查 stageFour 是否小于或等于当前日期。

Answer 2

// Our interval
const interval = setInterval(() => console.log('lalala'), 1000);

// Declare array of times
const times = [
  new Date ('March 8, 2021 00:00:00'),
  new Date('March 29,2021 00:00:00'),
  new Date('April 12, 2021 00:00:00'),
  new Date('March 3,2021 00:00:00'),
  new Date('June 21,2021 00:00:00'),
];



// Here begins the checking part.
// This would presumably be ran in a loop,
// perhaps in the same interval function?

// Declare the time we are checking against
const othertime = new Date();
// not needed if we want to just use Date.now()

// check against 
if (
  // use times.reduce to get earliest time
  times.reduce(
    // times.reduce is passed a function
    // that takes a and b as arguments
    (a, b) => (
      // check which time is smaller
      ( a.getTime() < a.getTime() )
      // and return that
      ? a : b
    )
    // compare the smallest time to the time we're checking against
  ).getTime() < othertime.getTime()
  // instead of othertime.getTime(), we can use Date.now()
) {
  // do whatever
  clearInterval(interval);
}

Answer 3

如果你想让你的 if 语句读起来更好，你可以创建一个小帮手

const stages = [stageOneA, stageOneB, stageTwo, stageThree, stageFour];
const olderThan = date => stage => stage <= date;

if(stages.some(olderThan(currentDate))) {
   clearInterval(updateCountdown);
}

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