JavaScript Basic Questions and Answers 3_Basic Knowledge

9. Comments in JavaScript
Q: How do I insert comments in JavaScript code?
A: JavaScript supports three different types of comments:
Multiline C-style comments. Content included in /* and */ are comments, for example:
/* This is a comment */
/* C-style comments can span
as many lines as you like,
as shown in this example */
C-style single-line comments. These comments start with // and end at the end of the line:
// This is a one-line comment
Use an HTML comment to start the sequence (). Consider this example:
This is also a one- line JS comment
because JS ignores the closing characters
of HTML-style comments
HTML-style comments are not common in JavaScript code. (//The single-line comment of the guide is simpler and more readable). However, it is highly recommended to use HTML comments to hide JavaScript code from older browsers.
10. Hidding JS code from old browsers (Hidding JS code from old browsers)
Q: How do I hide JS code from old versions that do not support JavaScript?
A: In order to prevent older browsers from displaying JS code, you can use the following method:
At the beginning of the

, your HTML file will contain the following code end:


Older versions of browsers will treat JS code as a long HTML comment. On the other hand, browsers that support JavaScript will interpret the JS code between
normally (the interpreter will treat the first and last lines in the JS code as single-line comments). Q: If the user's browser cannot execute JavaScript code, can I give the user a warning?
A: Of course, you can display a specific warning to users using non-JavaScript-compatible browsers. Place your warning message between

This page uses JavaScript

• 
  
• 
  Please use Netscape Navigator 3 or Internet Explorer 3

Make sure that JavaScript is enabled in your browser.

Browsers that support JavaScript will ignore the content between