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How to hide JavaScript code from older browsers that don't support JavaScript?

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2023-09-03 20:05:121211browse

如何对不支持 JavaScript 的旧浏览器隐藏 JavaScript 代码？

Older browsers sometimes don't understand JavaScript script tags. If not, they will only Ignore it and display your script as if it were part of the (X)HTML document body. it is A smart option to use comments to hide scripts in outdated browsers to prevent this from happening.

All modern browsers now support JavaScript; however, early browsers did not. at this In this article, we will learn how to prevent JavaScript code from executing in older browsers.

Because some of your viewers will be viewing the site on mobile phones, while others are using large desktops On the screen, a website cannot look exactly the same in all browsers. Likewise, some of your Users will use outdated browsers while others will use the latest browsers. Some Your users may be using a screen reader to hear your message read aloud, or may have Zoom in to read. Provides a defensive version of content that looks great Modern browsers, but still usable at a basic level for users of older browsers is the concept "Support everyone."

Strategy - We will use single-line HTML comments without a terminator ( 标签已打开。之后，我们将创建隐藏的 JavaScript 代码 来自早期的浏览器。在我们使用结束符之前，脚本将使用 标签结束 带注释的字符 (//->) after them.

grammar

<script>
   <!--
      // Your JavaScript code
      // that is hidden from older browser
      console.log("Tutorials Point");
   //-->
</script>

Example 1

In this example let us understand that if the browser is a browser that supports JavaScript, the background The color will change to red; otherwise, it will remain yellow. 

<!DOCTYPE html>
<html>
   <title>How can JavaScript code be hidden from old browsers that do not support JavaScript - TutorialsPoint</title>
<head>
   <meta charset="UTF-8">
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body bgcolor="green">
   <h1 style="text-align: center; font-size: 3rem;">
      Learn JavaScript with TutorialsPoint!
   </h1>
   <script type="text/javascript">
      <!--
         document.bgColor = "orange";
      //-->
   </script>
</body>
</html>

We can observe that outdated browsers ignore JavaScript code and treat it as HTML Note, while current browsers can access JavaScript code without any problem.

Displays orange when the browser supports JavaScript, as added in the style Example above.

Next, when the browser does not support JavaScript, it will be displayed in green, as added in the style the above example.

Example 2

For browsers that support JavaScript, this script hiding method also works. The first sum of the script The last few lines serve as titles. Client-side JavaScript interpreter understands HTML However, treat it like a single-line comment.

Therefore, the second line is treated as a single-line comment in browsers that support JavaScript. similar You can see that the line below starts with a single line comment string twice and therefore supports JavaScript The browser will also skip that line. Now only lines 3 to 5 are still running Executed as a JavaScript statement.

Although it takes some getting used to, this simple and elegant HTML and JavaScript comments achieve our desired goal of preventing JavaScript code from being displayed Browsers that don't support JavaScript. The use of this kind of comment is still very common Although fewer browsers now require it, it exists in JavaScript code across the internet. 

<!DOCTYPE html>
<html>
<title>How can JavaScript code be hidden from old browsers that do not support JavaScript - TutorialsPoint
</title>
<head>
   <meta charset="UTF-8">
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body style="text-align:center">
   <h2> Visit TutorialsPoint! </h2>
   <div id="result"> </div>
   <script langauge="JavaScript">
      <!-- start an HTML comment to hide the script
      // Here are the JavaScript statements.
      //
      //
      // close the HTML comment which hides the script -->
      const date = new Date();
      document.getElementById("result").innerHTML = (date);
   </script>
</body>
</html>

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