如何在 React JS 中实时显示时间和日期？

Question

简报：

您好，我创建了一个钩子useDate() 来显示当前时间和日期，如下所示：

interface ReturnDate {
  time: string;
  date: string;
  wish: string;
}

export const useDate = (): ReturnDate => {
  const locale = 'en';
  const today = new Date();

  const day = today.toLocaleDateString(locale, { weekday: 'long' });
  const date = `${day}, ${today.getDate()} ${today.toLocaleDateString(locale, { month: 'long' })}\n\n`;

  const hour = today.getHours();
  const wish = `Good ${(hour < 12 && 'Morning') || (hour < 17 && 'Afternoon') || 'Evening'}, `;

  const time = today.toLocaleTimeString(locale, { hour: 'numeric', hour12: true, minute: 'numeric' });

  return {
    date,
    time,
    wish,
  };
};

我在下面的组件中使用它，如下所示：

const ProfileGreetings: FC = () => {
  const { firstName } = useUserDetails();
  const { date, time, wish } = useDate();

  return (
    <div className="greetings-container">
      <h1>
        {wish}
        <PrimaryText text={`${firstName || ''}!`} />
      </h1>

      <div>
        <h3>
          {date}
          <br />
          {time}
        </h3>
      </div>
    </div>
  );
};

应用中的日期/时间格式：

8 月 2 日，星期日

晚上 11:54

问题陈述：

目前发生的情况是日期和时间在我刷新页面之前不会更新。有什么方法可以实时更新以下所有内容？

我正在考虑使用 每 1 分钟间隔一次来计算更新的时间和日期，但我真的不知道这是否是个好主意。我也不知道如何开始以及如何清除？

谢谢！ :)

Answer 1

由于您可以在自定义挂钩中使用挂钩，因此您可以创建一个间隔来每分钟更新一次，如下所示：

export const useDate = () => {
  const locale = 'en';
  const [today, setDate] = React.useState(new Date()); // Save the current date to be able to trigger an update

  React.useEffect(() => {
      const timer = setInterval(() => { // Creates an interval which will update the current data every minute
      // This will trigger a rerender every component that uses the useDate hook.
      setDate(new Date());
    }, 60 * 1000);
    return () => {
      clearInterval(timer); // Return a funtion to clear the timer so that it will stop being called on unmount
    }
  }, []);

  const day = today.toLocaleDateString(locale, { weekday: 'long' });
  const date = `${day}, ${today.getDate()} ${today.toLocaleDateString(locale, { month: 'long' })}\n\n`;

  const hour = today.getHours();
  const wish = `Good ${(hour < 12 && 'Morning') || (hour < 17 && 'Afternoon') || 'Evening'}, `;

  const time = today.toLocaleTimeString(locale, { hour: 'numeric', hour12: true, minute: 'numeric' });

  return {
    date,
    time,
    wish,
  };
};

Answer 2

我对此有一个想法。 我将在while 和动态睡眠上循环，currentTime 和currentTime + 1 second 以秒为单位的舍入之间的差异。你可以参考这个脚本。

function getRealTime() {
  const currentTime = Date.now();
  console.log(new Date(Math.round(currentTime / 1000) * 1000), currentTime);
  return (Math.floor(currentTime / 1000) + 1) * 1000 - currentTime;
}

(async function () {
  let reduceTime = 0;
  while (true) {
    reduceTime = getRealTime();
    await sleep(reduceTime);
  }
})()

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

Answer 3

import React from 'react';
import ReactDom from 'react-dom';

const date = new Date().toLocaleDateString();
const time = new Date().toLocaleTimeString();

ReactDom.render(
<>
<p>Today's date is {date}</p>
<p>Today's time is {time}</p>
</>
, 
document.getElementById('root'));

Output

Today's date is 8/14/2020

Today's time is 7:42:01 PM