JavaScript是一種常用的腳本語言，廣泛用於網頁互動性設計和開發。今天，我們將介紹一些JavaScript實作的實用功能實例。
JavaScript可用來建立簡單的計算器。程式碼段使用HTML中的按鈕和輸入框，以及JavaScript處理計算器的邏輯。使用者輸入數字、操作符和操作數，然後點擊等於號運行計算並顯示結果。
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Simple Calculator</title> </head> <body> <form name="calculator"> <input type="text" name="answer" id="answer"> <br> <input type="button" value=" 1 " onclick="calculator.answer.value += '1'"> <input type="button" value=" 2 " onclick="calculator.answer.value += '2'"> <input type="button" value=" 3 " onclick="calculator.answer.value += '3'"> <input type="button" value=" + " onclick="calculator.answer.value += '+'"> <br> <input type="button" value=" 4 " onclick="calculator.answer.value += '4'"> <input type="button" value=" 5 " onclick="calculator.answer.value += '5'"> <input type="button" value=" 6 " onclick="calculator.answer.value += '6'"> <input type="button" value=" - " onclick="calculator.answer.value += '-'"> <br> <input type="button" value=" 7 " onclick="calculator.answer.value += '7'"> <input type="button" value=" 8 " onclick="calculator.answer.value += '8'"> <input type="button" value=" 9 " onclick="calculator.answer.value += '9'"> <input type="button" value=" * " onclick="calculator.answer.value += '*'"> <br> <input type="button" value=" c " onclick="calculator.answer.value = ''"> <input type="button" value=" 0 " onclick="calculator.answer.value += '0'"> <input type="button" value=" = " onclick="calculator.answer.value = eval(calculator.answer.value)"> <input type="button" value=" / " onclick="calculator.answer.value += '/'"> <br> </form> </body> </html>
JavaScript可用於建立倒數計時器，即從指定的日期和時間開始倒數計時，直到特定目標時間。此程式碼段使用Date物件來取得目前時間和目標時間，計算差異，並將其顯示在HTML頁面上。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>CountDown Timer</title>
</head>
<body>
<div id="countdown"></div>
<script>
// Set the date we're counting down to
var countDownDate = new Date("Jan 1, 2022 00:00:00").getTime();
// Update the count down every 1 second
var x = setInterval(function() {
// Get today's date and time
var now = new Date().getTime();
// Find the distance between now and the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Output the result in an element with id="countdown"
document.getElementById("countdown").innerHTML = days + "d " + hours + "h "
+ minutes + "m " + seconds + "s ";
// If the count down is over, write some text
if (distance < 0) {
clearInterval(x);
document.getElementById("countdown").innerHTML = "EXPIRED";
}
}, 1000);
</script>
</body>
</html>JavaScript可用於建立圖片輪播器，其中一組圖像輪流顯示在網頁上。此程式碼片段使用HTML中的圖像元素和JavaScript邏輯，以陣列儲存圖像列表，並在指定的時間間隔內更新目前圖像。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Image Slider</title>
</head>
<body>
<div id="slider">
<img id="sliderImg" src="">
</div>
<script>
var images = [
"img1.jpg", "img2.jpg", "img3.jpg", "img4.jpg"
];
var current = 0;
function changeImage(){
current++;
if(current >= images.length){
current = 0;
}
document.getElementById("sliderImg").src = images[current];
}
setInterval(changeImage, 3000);
</script>
</body>
</html>JavaScript可用來驗證使用者輸入，以確保輸入資料的格式和內容正確。程式碼段使用HTML表單元素和JavaScript邏輯，透過檢查每個表單元素來驗證使用者輸入。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Form Validation</title>
<style>
.error{
color: red;
}
</style>
</head>
<body>
<form id="myForm">
<label for="name">Name:</label>
<input type="text" id="name" name="name"><br>
<label for="email">Email:</label>
<input type="email" id="email" name="email"><br>
<label for="phone">Phone:</label>
<input type="text" id="phone" name="phone"><br>
<input type="submit" value="Submit">
</form>
<script>
document.getElementById("myForm").addEventListener("submit", function(event){
var name = document.getElementById("name").value;
var email = document.getElementById("email").value;
var phone = document.getElementById("phone").value;
var nameError = document.getElementById("nameError");
var emailError = document.getElementById("emailError");
var phoneError = document.getElementById("phoneError");
if(!name){
nameError.innerHTML = "Please enter your name.";
event.preventDefault();
}
if(!email){
emailError.innerHTML = "Please enter your email.";
event.preventDefault();
}
if(!phone){
phoneError.innerHTML = "Please enter your phone number.";
event.preventDefault();
}
});
</script>
</body>
</html>總結
這些是JavaScript實作的功能實例，涵蓋了計算器、倒數計時器、圖片輪播器和表單驗證等實用功能。當然，這只是JavaScript應用程式的冰山一角，JavaScript在Web設計和開發上有著許多其他用途和應用場景。
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