新手村29 - Countdown Timer

11th鐵人賽 javascript 前端新手村

Chester

2019-10-14 08:37:36

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29 - Countdown Timer

俗話說的好，一天一蘋果，醫生遠離我

一天一 JS，What the f*ck JavaScript？

small steps every day - 記錄著新手村日記

完成目標

做一個倒數計時器

功能
- 各種設定好的時間可以進行倒數
- 可以客製化時間倒數
畫面
- 顯示目前倒數的數字
- 顯示倒數結束時是幾點幾分

index_START.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Countdown Timer</title>
  <link href='https://fonts.googleapis.com/css?family=Inconsolata' rel='stylesheet' type='text/css'>
  <link rel="stylesheet" href="style.css">
</head>
<body>
  <div class="timer">
    <div class="timer__controls">
      <button data-time="20" class="timer__button">20 Secs</button>
      <button data-time="300" class="timer__button">Work 5</button>
      <button data-time="900" class="timer__button">Quick 15</button>
      <button data-time="1200" class="timer__button">Snack 20</button>
      <button data-time="3600" class="timer__button">Lunch Break</button>
      <form name="customForm" id="custom">
        <input type="text" name="minutes" placeholder="Enter Minutes">
      </form>
    </div>
    <div class="display">
      <h1 class="display__time-left"></h1>
      <p class="display__end-time"></p>
    </div>
  </div>

  <script src="scripts-START.js"></script>
</body>
</html>

Style.css

html {
  box-sizing: border-box;
  font-size: 10px;
  background: #8E24AA;
  background: linear-gradient(45deg,  #42a5f5 0%,#478ed1 50%,#0d47a1 100%);
}

*, *:before, *:after {
  box-sizing: inherit;
}

body {
  margin: 0;
  text-align: center;
  font-family: 'Inconsolata', monospace;
}

.display__time-left {
  font-weight: 100;
  font-size: 20rem;
  margin: 0;
  color: white;
  text-shadow: 4px 4px 0 rgba(0,0,0,0.05);
}

.timer {
  display: flex;
  min-height: 100vh;
  flex-direction: column;
}

.timer__controls {
  display: flex;
}

.timer__controls > * {
  flex: 1;
}

.timer__controls form {
  flex: 1;
  display: flex;
}

.timer__controls input {
  flex: 1;
  border: 0;
  padding: 2rem;
}

.timer__button {
  background: none;
  border: 0;
  cursor: pointer;
  color: white;
  font-size: 2rem;
  text-transform: uppercase;
  background: rgba(0,0,0,0.1);
  border-bottom: 3px solid rgba(0,0,0,0.2);
  border-right: 1px solid rgba(0,0,0,0.2);
  padding: 1rem;
  font-family: 'Inconsolata', monospace;
}

.timer__button:hover,
.timer__button:focus {
  background: rgba(0,0,0,0.2);
  outline: 0;
}

.display {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.display__end-time {
  font-size: 4rem;
  color: white;
}

scripts-START.js

空

JS - step by step

首先，我們先將需要的元素選取起來，必須先找到點擊的按鈕、點擊按鈕後會觸發的 h1、 p

let countdown;
const timerDisplay = document.querySelector('.display__time-left');
const endTime = document.querySelector('.display__end-time');
const buttons = document.querySelectorAll('[data-time]');

console.log(timerDisplay);
	//<h1 class="display__time-left"></h1>
console.log(endTime);
  //<p class="display__end-time"></p>
console.log(buttons);
	//NodeList(5) [button.timer__button, button.timer__button, button.timer__button, button.timer__button, button.timer__button]

接下來，當我們觸發點擊按鈕時，我們應該先要取得現在的時間、取得倒數的時間長度、執行倒數計時、顯示剩餘的時間於 h1，顯示結束時間於 p，變數 seconds 為取得 data-attibute 中所代表的倒數計時時間並轉為數字；其中在呼叫方法 timer 之前，我們必須先執行一次 clearInterval() 將先前的 setInterval() 方法先清除掉（後續避免會有BUG），變數 now 為取得目前的時間，變數 then 為將取得的時間轉換為秒數

function startTimer() {
  const seconds = parseInt(this.dataset.time);
  timer(seconds);
}

function timer(seconds) {
  clearInterval(countdown);

  const now = Date.now();
  const then = now + seconds * 1000;
  displayTimeLeft(seconds);
  displayEndTime(then);

  countdown = setInterval(() => {
    const secondsLeft = Math.round((then - Date.now()) / 1000);
    if(secondsLeft < 0) {
      clearInterval(countdown);
      return;
    }
    displayTimeLeft(secondsLeft);
  }, 1000);
}

接下來來完成 Function 中的 displayTimeLeft 與 displayEndTime ，一個為計算倒數計時的大標題 h1 ，另一個為計算結束時間為何，讓使用者可以知道倒數終止的時間為幾點幾分

function displayTimeLeft(seconds) {
  const minutes = Math.floor(seconds / 60);
  const remainderSeconds = seconds % 60;
  const display = `${minutes}:${remainderSeconds < 10 ? '0' : '' }${remainderSeconds}`;
  document.title = display;
  timerDisplay.textContent = display;
}

function displayEndTime(timestamp) {
  const end = new Date(timestamp);
  const hour = end.getHours();
  const adjustedHour = hour > 12 ? hour - 12 : hour;
  const minutes = end.getMinutes();
  endTime.textContent = `Be Back At ${adjustedHour}:${minutes < 10 ? '0' : ''}${minutes}`;
}

最後，再加上讓使用者可以自己輸入時間的 submit 按鈕，可以客製化自己想要多少的時間

document.customForm.addEventListener('submit', function(e) {
  e.preventDefault();
  const mins = this.minutes.value;
  console.log(mins);
  timer(mins * 60);
  this.reset();
});

就大功告成啦！

JS - final

let countdown;
const timerDisplay = document.querySelector('.display__time-left');
const endTime = document.querySelector('.display__end-time');
const buttons = document.querySelectorAll('[data-time]');

buttons.forEach(button => button.addEventListener('click', startTimer));

function startTimer() {
  const seconds = parseInt(this.dataset.time);
  timer(seconds);
}

function timer(seconds) {
  // clear any existing timers
  clearInterval(countdown);

  const now = Date.now();
  const then = now + seconds * 1000;
  displayTimeLeft(seconds);
  displayEndTime(then);

  countdown = setInterval(() => {
    const secondsLeft = Math.round((then - Date.now()) / 1000);
    // check if we should stop it!
    if(secondsLeft < 0) {
      clearInterval(countdown);
      return;
    }
    // display it
    displayTimeLeft(secondsLeft);
  }, 1000);
}

function displayTimeLeft(seconds) {
  const minutes = Math.floor(seconds / 60);
  const remainderSeconds = seconds % 60;
  const display = `${minutes}:${remainderSeconds < 10 ? '0' : '' }${remainderSeconds}`;
  document.title = display;
  timerDisplay.textContent = display;
}
  
function displayEndTime(timestamp) {
  const end = new Date(timestamp);
  const hour = end.getHours();
  const adjustedHour = hour > 12 ? hour - 12 : hour;
  const minutes = end.getMinutes();
  endTime.textContent = `Be Back At ${adjustedHour}:${minutes < 10 ? '0' : ''}${minutes}`;
}

本刊同步於個人網站：http://chestertang.site/

本次範例程式碼原作者來源：https://tinyurl.com/yavm5f5n