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 id="This-nbsp-is-nbsp-a-nbsp-heading">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</script>
如需在 HTML 页面中插入 JavaScript，请使用 <script> 标签。</script>
<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。</script>
中的 JavaScript在本例中，JavaScript 会在页面加载时向 HTML 的
写文本：实例
. . <script> document.write("<h1 id="This-nbsp-is-nbsp-a-nbsp-heading">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 id="My-nbsp-Web-nbsp-Page">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 id="My-nbsp-Web-nbsp-Page">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 <script> 标签的 "src" 属性中设置该 .js 文件：</script>
实例
<!DOCTYPE html> <html> <body> <script src="myScript.js"></script> </body> </html>
在
或 中引用脚本文件都是可以的。实际运行效果与您在 <script> 标签中编写脚本完全一致。<p>提示：外部脚本不能包含 <script> 标签。<p>以上就是网站开发 | JavaScript 教程的内容，更多相关内容请关注PHP中文网（www.php.cn）！<p><br/></script>
From Websites to Apps: The Diverse Applications of JavaScriptApr 22, 2025 am 12:02 AMJavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.
Python vs. JavaScript: Use Cases and Applications ComparedApr 21, 2025 am 12:01 AMPython is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.
The Role of C/C in JavaScript Interpreters and CompilersApr 20, 2025 am 12:01 AMC and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.
JavaScript in Action: Real-World Examples and ProjectsApr 19, 2025 am 12:13 AMJavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.
JavaScript and the Web: Core Functionality and Use CasesApr 18, 2025 am 12:19 AMThe main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.
Understanding the JavaScript Engine: Implementation DetailsApr 17, 2025 am 12:05 AMUnderstanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.
Python vs. JavaScript: The Learning Curve and Ease of UseApr 16, 2025 am 12:12 AMPython is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.
Python vs. JavaScript: Community, Libraries, and ResourcesApr 15, 2025 am 12:16 AMPython and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.
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DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
