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javascript-How to design a countdown program using javascript

王林Original: 2023-05-29 15:46:08867browse

With the busyness of our modern life, people often need an accurate timing tool. The countdown program is such a practical tool that can help us count down accurately so that we can better organize our time. In this article, I will show you how to design a countdown program using JavaScript.

Preparation

First, we need to create a basic HTML file and add a countdown area and a button to it. The countdown area will be used to display the countdown time, and the button will be used to start the countdown. The following is the HTML code:

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>倒计时程序</title>
  </head>
  <body>
    <div id="countdown"></div>
    <button onclick="startCountdown()">开始倒计时</button>
  </body>
</html>

In the above code, we use a div element to display the countdown time and add a button to start the countdown. When the button is clicked, a JavaScript function startCountdown() is called.

Write JavaScript code

Now, we need to write JavaScript code to design the countdown program. The program will use the Date object to calculate the time and display it in the countdown area. The following is the JavaScript code:

function startCountdown() {
  // 设置倒计时时间（秒数）
  var countdownTime = 60;

  // 获取当前时间
  var now = new Date().getTime();

  // 计算倒计时结束时间
  var countdownEnd = now + (countdownTime * 1000);

  // 更新倒计时区域
  var countdownElement = document.getElementById('countdown');
  var countdownInterval = setInterval(function() {
    // 获取当前时间
    var now = new Date().getTime();

    // 计算剩余时间
    var countdownRemaining = countdownEnd - now;

    // 将剩余时间转换成分、秒格式
    var minutes = Math.floor((countdownRemaining % (1000 * 60 * 60)) / (1000 * 60));
    var seconds = Math.floor((countdownRemaining % (1000 * 60)) / 1000);

    // 更新倒计时区域
    countdownElement.innerHTML = minutes + " 分钟 " + seconds + " 秒 ";

    // 当倒计时结束，清除计时器
    if (countdownRemaining <= 0) {
      clearInterval(countdownInterval);
      countdownElement.innerHTML = "倒计时结束！";
    }
  }, 1000);
}

In the above code, we have called the startCountdown() function from the button. This function first sets the countdown time (60 seconds) and obtains the current time. Next, it calculates the time until the countdown ends and saves it in the countdownEnd variable.

Then, the function uses the setInterval() function to periodically update the countdown area. In each interval, it gets the current time and calculates the remaining time. It then converts the remaining time into formatted minutes and seconds and updates it into the countdown area. Finally, when the countdown ends, it clears the timer and sets the countdown area to "Countdown over!".

Test program

Now, we have completed the design of the countdown program. Let's open the HTML file and test whether the program works properly. When we click the "Start Countdown" button, the countdown program will start working and display the "Countdown Ended!" message after 60 seconds. If you want to change the countdown time, update the value of the countdownTime variable in the startCountdown function.

Conclusion

By using JavaScript, we can easily design a countdown program to help us manage time better. The countdown program can be used in various situations, such as exams, fitness, rest, etc. I hope this article can help you learn how to use JavaScript to design a countdown program and apply it to real life.

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JavaScript html date 对象

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