javascript - 为什么我们在 Countdown App 中使用 Remainder？

Question

我观看了构建 Countdown 应用程序的 JavaScript 教程。对于JS，我们在下面写了这段代码。但我不明白为什么我们需要取余数 % 然后除以更大的单位？有人可以解释一下吗？这部分我特别不明白......

  //Calculate 🧮
  const textDay = Math.floor(gap / day);
  const textHour = Math.floor((gap % day) / hour);
  const textMinute = Math.floor((gap % hour) / minute);
  const textSecond = Math.floor((gap % minute) / second);

//Basically we are getting the difference between the FUTURE and NOW . and ➖ substract the difference

const countdown = () => {
  const countDate = new Date("May 17, 2021 00:00:00").getTime();
  const now = new Date().getTime();
  const gap = countDate - now;

  //How does the time work❓
  const second = 1000;
  const minute = second * 60; //60000
  const hour = minute * 60; //3600000
  const day = hour * 24;

  //Calculate 🧮
  const textDay = Math.floor(gap / day);
  const textHour = Math.floor((gap % day) / hour);
  const textMinute = Math.floor((gap % hour) / minute);
  const textSecond = Math.floor((gap % minute) / second);

  //Update our actual HTML
  document.querySelector(".day").innerText = textDay;
  document.querySelector(".hour").innerText = textHour;
  document.querySelector(".minute").innerText = textMinute;
  document.querySelector(".second").innerText = textSecond;
};

setInterval(countdown, 1000); 

Answer 1

间隔以毫秒为单位。如果你得到 gap % day 的余数和 day是每天的毫秒数，那么您将获得不适合整天的所有内容 => 所有较小的单位(小时、分钟、秒和毫秒)。
例如。:

const countdown = () => {
  // Lets just say gap is 5.5 days = 5.5 * 24 * 60 * 60 * 1000 milliseconds
  const gaps = 475200000;

  // These are the equivalents of the time units in milliseconds
  const second = 1000;        // =     1000 ms
  const minute = second * 60; // =    60000 ms
  const hour = minute * 60;   // =  3600000 ms
  const day = hour * 24;      // = 86400000 ms

  //Calculate 🧮
  const textDay = Math.floor(gap / day); // This will return 5 days
  
  let remainder = gap % day; // This will be 5.5 % 1 = 0.5 days or 43200000 ms
  const textHour = Math.floor(remainder / hour); // This will return 12 hours
  
  // gap = 5.5 days = 132 hours
  remainder = gap % hour; // This will be 132 % 1 = 0
  const textMinute = Math.floor(remainder / minute); // This will return 0

  // gap = 5.5 days = 7920 minutes
  remainder = gap % minutes; // This will be 7920 % 1 = 0
  const textSecond = Math.floor(remainder  / second); // This will return 0

  //Update our actual HTML
  document.querySelector(".day").innerText = textDay;
  document.querySelector(".hour").innerText = textHour;
  document.querySelector(".minute").innerText = textMinute;
  document.querySelector(".second").innerText = textSecond;
};