Where are the JavaScript settings-Front-end Q&A-php.cn

Where are the JavaScript settings

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Release： 2023-04-24 11:21:30

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JavaScript is a flexible programming language that is widely used in web development, mobile applications, and server-side programming. It can enhance the interactivity and dynamics of web pages, making users more comfortable, rich and faster when browsing web pages. However, for JavaScript to be executed correctly by the browser, it must be placed in the correct location.

JavaScript setting location

There are three main JavaScript setting locations:

1. Inline setting

Inline setting is to embed JavaScript code directly Into the tags in the HTML document, the method is relatively simple, but it is not recommended because it will seriously affect the readability and maintainability of the HTML document.

For example:

<button onclick="alert(&#39;Hello, World!&#39;)">Click me!</button>

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When this button is clicked, a warning box will pop up.

2. Internal settings

This setting method is to write JavaScript code in the <head> or <body> of the HTML document Within the <script> tag in the tag. This setting can be placed either in the header or in the body part. The advantage of internal settings is that it can improve the readability and maintainability of HTML documents. In some cases, it can improve the access speed of the website because the js code will be cached, thereby reducing the pressure on the server.

For example:

<html>
  <head>
    <script type="text/javascript">
      function greeting() {
        alert('Hello, World!');
      }
    </script>
  </head>
  <body>
    <button onclick="greeting()">Say hello</button>
  </body>
</html>

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This script is defined at the head of the document, but used in the body of the document.

3. External settings

This setting method is to write the JavaScript code in a separate <.js> file, and use <script&gt ; tags are introduced into HTML documents. This setting method can achieve code reuse and overall optimization, and is more suitable for large websites and websites that require frequent updates.

For example: The HTML document structure is as follows

<!DOCTYPE html>
<html>
  <head>
    <script src="script.js"></script>
  </head>
  <body>
    <button onclick="greeting()">Say hello</button>
  </body>
</html><p> Among them, the src attribute of the <code><script></code> tag specifies the introduction of a JavaScript file. The content of the file is as follows </p>
<pre class="brush:php;toolbar:false">function greeting() {
  alert('Hello, World!');
}

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This script exists alone in the external script.js file.

Summary

No matter which method is used, it should be placed in <body> or <head> (preferably in <body>) so that the browser can correctly parse and execute JavaScript code. When there is a lot of JavaScript code, it is recommended to use external settings to improve the maintainability and overall performance of the code. At the same time, we also need to pay attention to compatibility issues. Different browsers may parse and execute the same piece of JavaScript code differently.

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