How To Write Comments in JavaScript
Comments in JavaScript
JavaScript comments describe and explain code and improve readability. A comment is a statement that is not executed. The JavaScript interpreter skips comments, so they don't affect runtime.
Why Use Comments?
Comments add details, warnings, and suggestions so users and other developers can understand the code.
There are 3 types of comments in JavaScript:
- Single-Line Comment
- Multi-Line Comment
- ScriptDoc Comment
1. Single-Line Comment
Single-line comments use double forward slashes // and can appear before any statement.
<script>
// Write on browser
document.write("Hello Javascript!");
// Write text in <h2> Heading
document.write("<h2> Hello Javascript! </h2>");
</script>Output:
Hello Javascript!
Hello Javascript!
2. Multi-Line Comment
Multi-line comments are used for longer descriptions. They start with /* and end with */.
Note: Multi-line comments can also be used for single-line comments if you prefer.
<script>
/*
First line: Write Simple write
Second line: Write text in <h2> Heading
*/
document.write("Hello World!");
document.write("<h2> Hello World! </h2>");
</script>Output:
Hello World!
Hello World!
3. ScriptDoc Comment / JavaScript Documentation
ScriptDoc (JSDoc) is a JavaScript documentation technique for documenting functions, parameters, return values, and more.
Best Practice: Use JSDoc comments to document functions, arguments, and return types for better code maintainability.
Syntax:
<script>
/**
* ScriptDoc technique to write comment
* @TagName Description
* @author
* @version
* ….
**/
</script>Complete Example:
<script>
/**
* Multiplication of two numbers
* @param {Number} a - First number
* @param {Number} b - Second number
* @return {String} mult - Result of multiplication
**/
function multiplication(a, b) {
mult = a * b;
return "Output is : " + mult.toString();
}
result = multiplication(7, 10);
document.write(result);
</script>Output:
Output is : 70
ScriptDoc Tags Reference
Common JSDoc tags for documenting JavaScript:
| Tag | Description |
|---|---|
@author |
Author of JavaScript file, functions, class |
@classDescription |
Brief description of the Class |
@constructor |
Specifies this function is a constructor |
@example |
Describe a real example for how to use this function |
@method |
Specifies the method name in class |
@param |
Specifies parameter of this function |
@private |
Indicates that a class or function is private |
@property |
Indicates specified property are instance of the class |
@return |
Specifies the return values of a function |
@type |
Specify the data type of this property |
@version |
Specify the version number of file |
Comment Types Comparison
| Comment Type | Syntax | Best For |
|---|---|---|
| Single-Line | // comment |
Quick notes, inline explanations |
| Multi-Line | /* comment */ |
Longer explanations, disabling code |
| JSDoc | /** */ |
Function documentation, API generation |
Best Practices
✅ Do's
- • Document complex logic
- • Explain "why", not just "what"
- • Use JSDoc for functions
- • Keep comments up-to-date
❌ Don'ts
- • Don't state the obvious
- • Avoid outdated comments
- • Don't over-comment simple code
- • Remove commented-out code
Summary
JavaScript comments improve code readability. Use single-line comments (//) for short notes, multi-line comments (/* */) for longer descriptions, and JSDoc comments (/** */) for function documentation.
Good commenting practices improve maintainability and help other developers understand your code.