Website Development | JavaScript Tutorials
JavaScript is the most popular programming language in the world. This language can be used in HTML and the web, and can be used on a wide range of devices such as servers, PCs, laptops, tablets, and smartphones.
JavaScript is a scripting language
JavaScript is a lightweight programming language.
JavaScript is programming code that can be inserted into HTML pages.
JavaScript, when inserted into an HTML page, can be executed by all modern browsers.
JavaScript: Writing HTML Output
Example
document.write("<h1>This is a heading</h1>");
document.write("<p>This is a paragraph</p>");Tip: You can only use document.write with HTML output. If you use this method after the document is loaded, the entire document will be overwritten.
JavaScript: Reacting to Events
Example
<button type="button" onclick="alert('Welcome!')">点击这里</button>
alert() function is not commonly used in JavaScript, but it is very convenient for code testing . The
onclick event is just one of many events you'll learn about in this tutorial.
JavaScript: Changing HTML content
Using JavaScript to process HTML content is a very powerful feature.
Example
x=document.getElementById("demo") //查找元素x.innerHTML="Hello JavaScript"; //改变内容You will often see document.getElementByID("some id"). This method is defined in the HTML DOM. DOM (Document Object Model) is the official W3C standard for accessing HTML elements.
JavaScript: Change HTML style
Changing the style of HTML elements is a variant of changing HTML attributes.
Example
x=document.getElementById("demo") //找到元素x.style.color="#ff0000"; //改变样式JavaScript: Validating input
JavaScript is often used to validate user input.
实例
if isNaN(x) {alert("Not Numeric")};您知道吗？
提示：JavaScript 与 Java 是两种完全不同的语言，无论在概念还是设计上。
Java（由 Sun 发明）是更复杂的编程语言。
ECMA-262 是 JavaScript 标准的官方名称。
JavaScript 由 Brendan Eich 发明。它于 1995 年出现在 Netscape 中（该浏览器已停止更新），并于 1997 年被 ECMA（一个标准协会）采纳。
JavaScript 使用
HTML 中的脚本必须位于 <script> 与 </script> 标签之间。
脚本可被放置在 HTML 页面的 和 部分中。
<script> 标签</strong></p><p>如需在 HTML 页面中插入 JavaScript，请使用 <script> 标签。</p><p><script> 和 </script> 会告诉 JavaScript 在何处开始和结束。
<script> 和 </script> 之间的代码行包含了 JavaScript：
<script>
alert("My First JavaScript");
</script>您无需理解上面的代码。只需明白，浏览器会解释并执行位于 <script> 和 </script> 之间的 JavaScript。
那些老旧的实例可能会在 <script> 标签中使用 type="text/javascript"。现在已经不必这样做了。JavaScript 是所有现代浏览器以及 HTML5 中的默认脚本语言。</p><p style="margin: 0px; padding: 0px; font-weight: 400; font-size: 16px; max-width: 100%; color: rgb(62, 62, 62); font-family: -apple-system-font, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif; white-space: normal; background-color: rgb(255, 255, 255); box-sizing: border-box !important; word-wrap: break-word !important;"><body> 中的 JavaScript</p><p>在本例中，JavaScript 会在页面加载时向 HTML 的 <body> 写文本：</p><p style="margin: 20px 0px 0px; padding: 0px; font-size: 12px; max-width: 100%; color: rgb(62, 62, 62); font-family: -apple-system-font, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif; white-space: normal; background-color: rgb(255, 255, 255); border: 0px; box-sizing: border-box !important; word-wrap: break-word !important;">实例</p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'><!DOCTYPE html> <html> <body> . . <script> document.write("<h1>This is a heading</h1>"); document.write("<p>This is a paragraph</p>"); </script> . .
JavaScript 函数和事件
上面例子中的 JavaScript 语句，会在页面加载时执行。
通常，我们需要在某个事件发生时执行代码，比如当用户点击按钮时。
如果我们把 JavaScript 代码放入函数中，就可以在事件发生时调用该函数。
您将在稍后的章节学到更多有关 JavaScript 函数和事件的知识。
或 中的 JavaScript
您可以在 HTML 文档中放入不限数量的脚本。
脚本可位于 HTML 的
或 部分中，或者同时存在于两个部分中。通常的做法是把函数放入
部分中，或者放在页面底部。这样就可以把它们安置到同一处位置，不会干扰页面的内容。中的 JavaScript 函数
在本例中，我们把一个 JavaScript 函数放置到 HTML 页面的
部分。该函数会在点击按钮时被调用：
实例
<!DOCTYPE html>
<html>
<head><script>
function myFunction()
{
document.getElementById("demo").innerHTML="My First JavaScript Function";
}
</script></head>
<body>
<h1>My Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try it</button>
</body>
</html>中的 JavaScript 函数
在本例中，我们把一个 JavaScript 函数放置到 HTML 页面的
部分。该函数会在点击按钮时被调用：
实例
<!DOCTYPE html>
<html>
<body>
<h1>My Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try it</button><script>
function myFunction()
{
document.getElementById("demo").innerHTML="My First JavaScript Function";
}
</script></body>
</html>提示：我们把 JavaScript 放到了页面代码的底部，这样就可以确保在
元素创建之后再执行脚本。
外部的 JavaScript
也可以把脚本保存到外部文件中。外部文件通常包含被多个网页使用的代码。
外部 JavaScript 文件的文件扩展名是 .js。
如需使用外部文件，请在
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