第20天的挑战是，设置一个倒计时时间，接下来开始倒计时。
<!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>
</body>
</html>- 上面的
button中自定义的data-time为倒计时时间，以秒为单位。 form为自定义倒计时时间，以分为单位。- class为
display__time-left的div主要为了展示倒计时的动态。 - class为
display__end-time的div主要为了展示倒计时什么时候结束。
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;
}let countdown;
const timerDisplay = document.querySelector('.display__time-left');
const endTime = document.querySelector('.display__end-time');
const buttons = document.querySelectorAll('[data-time]');
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' : ''}${minutes}`;
}
function startTimer() {
const seconds = parseInt(this.dataset.time);
timer(seconds);
}
buttons.forEach(button => button.addEventListener('click', startTimer));
document.customForm.addEventListener('submit', function (e) {
e.preventDefault();
const mins = this.minutes.value;
console.log(mins);
timer(mins * 60);
this.reset();
});逻辑分析：
- 当点击button按钮时，调用
startTimer方法。
buttons.forEach(button => button.addEventListener('click', startTimer));- 在输入框中自定义倒计时时间时，输入
enter时调用传入的回调函数。
document.customForm.addEventListener('submit', function (e) {
e.preventDefault();
const mins = this.minutes.value;
console.log(mins);
timer(mins * 60);
this.reset();
});- startTimer函数代码解释
function startTimer() {
<!--获取当前点击的button的data-time值，并将其转换成整数-->
const seconds = parseInt(this.dataset.time);
<!--调用timer函数-->
timer(seconds);
}- displayTimeLeft代码
<!--计算时分秒，并且展示-->
function displayTimeLeft(seconds) {
const minutes = Math.floor(seconds / 60);
const remainderSeconds = seconds % 60;
const display = `${minutes}:${remainderSeconds < 10 ? '0' : '' }${remainderSeconds}`;
document.title = display;
timerDisplay.textContent = display;
}- displayEndTime代码
<!--计算倒计时结束时间，并且展示-->
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}`;
}- timer代码
function timer(seconds) {
// clear any existing timers
清除正在进行的倒计时
clearInterval(countdown);
<!--获取当前时间-->
const now = Date.now();
<!--计算多少毫秒后结束倒计时-->
const then = now + seconds * 1000;
<!--调用displayTimeLeft函数展示倒计时效果-->
displayTimeLeft(seconds);
<!--展示结束时间-->
displayEndTime(then);
<!--设置定时器，更新倒计时组建-->
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);
}