JavaScript is a widely used programming language for web development and application development. In web development, JavaScript is often embedded into HTML pages to achieve interactivity and dynamic effects. However, JavaScript code can be embedded from a variety of sources, including inline, external files, and frames. In this article, we will explore where JavaScript code is embedded and how to use it in web development.
1. Inline JavaScript
Inline JavaScript refers to writing JavaScript code directly into the HTML document. This method is the simplest to use and is suitable for situations where there is only a small amount of JavaScript code. The way to embed JavaScript code into a document is to include it in a <script> tag, as shown below: </script>
<html>
<head>
<title>内联 JavaScript示例</title>
</head>
<body>
<h1 id="内联-JavaScript示例">内联 JavaScript示例</h1>
<p>当前时间是：</p>
<script>
var now = new Date();
document.write(now);
</script>
</body>
</html>In the above example, we embed a simple JavaScript script into an HTML document. This script gets the current date and writes it into the document. In this example, the JavaScript code is written directly in the <script> tag. The advantage of this method is that it is simple and easy to use, and is suitable for situations where there is only a small amount of JavaScript code. However, it is not suitable for complex JavaScript applications because in this case the code will become difficult to maintain and manage. </script>
2. External JavaScript files
External JavaScript files refer to storing JavaScript codes in separate files and referencing them from HTML pages. The main advantage of this approach is that it makes JavaScript code easier to maintain and manage. The syntax for using external JavaScript files is similar to inline JavaScript, except that the code is no longer placed in the HTML document, but in a separate .js file. Here is a simple example:
<html>
<head>
<title>外部 JavaScript示例</title>
<script src="script.js"></script>
</head>
<body>
<h1 id="外部-JavaScript示例">外部 JavaScript示例</h1>
<p>当前时间是：</p>
<script>
updateTime();
</script>
</body>
</html>In the above example, we stored the JavaScript code in a file called script.js and referenced it from the HTML document. The JavaScript code gets the current time from the file and writes it to the document. In the HTML document, we use the <script> tag to call a JavaScript function called updateTime(). </script>
3. Use frameworks
In web development, we often use JavaScript frameworks to simplify code writing and management. A framework is a set of JavaScript code written by other developers designed to meet the needs of a specific web application. Frameworks generally provide various functions and methods that make it easier for developers to create interactive web applications.
Common JavaScript frameworks include jQuery, React and Vue.js. These frameworks provide a variety of features, including DOM manipulation, Ajax calls, and dynamic effects. The following is an example using the jQuery framework:
<html>
<head>
<title>使用 jQuery框架示例</title>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
</head>
<body>
<h1 id="使用-jQuery框架示例">使用 jQuery框架示例</h1>
<p>当前时间是：</p>
<script>
$(document).ready(function(){
var now = new Date();
$("p").append(now);
});
</script>
</body>
</html>In the above example, we referenced the jQuery framework and wrote JavaScript code in the $(document).ready() function. This code gets the current time and appends it to the
element in the HTML document. This example demonstrates how to use the jQuery framework to write JavaScript code in a concise way.
Summary
JavaScript can be embedded in different ways, including inline, external files, and frames. In web development, we can choose the method that suits us according to the usage situation. Although inline JavaScript is the simplest, it is not suitable for complex JavaScript applications. Using external files allows for better code management and maintenance, while frameworks simplify the entire development process and increase developer efficiency. No matter which approach you take, JavaScript is an indispensable tool in web development.
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