JavaScript comments are an essential part of any codebase. They allow developers to add explanatory notes, provide context, or temporarily disable specific sections of code without affecting the functionality of the program. In this article, we will explore the different types of JavaScript comments and provide examples of their usage.
Single-line Comments
The most common type of JavaScript comment is the single-line comment. It is used to add comments on a single line and is denoted by two forward slashes (//) followed by the comment text. Single-line comments are often used to explain the purpose of a particular line of code or to provide additional information.
Example:
// This variable stores the user's name
let userName = "John Doe";
In the example above, the single-line comment clarifies the purpose of the variable userName by indicating that it stores the user’s name.
Multi-line Comments
Multi-line comments, also known as block comments, are used to add comments that span multiple lines. They are denoted by a forward slash followed by an asterisk (/*) to start the comment and an asterisk followed by a forward slash (*/) to end the comment. Multi-line comments are often used to provide detailed explanations or to temporarily disable larger sections of code.
Example:
/*
This function calculates the sum of two numbers.
Parameters:
- num1: the first number
- num2: the second number
Returns: the sum of num1 and num2
*/
function calculateSum(num1, num2) {
return num1 + num2;
}
In the example above, the multi-line comment provides a description of the calculateSum function, including its parameters and return value.
Documenting Comments
Documenting comments, also known as JSDoc comments, are a specific type of comment used to generate documentation from the code. They follow a specific syntax and can include additional information such as function descriptions, parameter types, and return types. Documenting comments are commonly used in larger codebases or when generating documentation using tools like JSDoc.
Example:
/**
* Calculates the factorial of a given number.
* @param {number} n - The number to calculate the factorial for.
* @returns {number} The factorial of the input number.
*/
function factorial(n) {
if (n === 0 || n === 1) {
return 1;
} else {
return n * factorial(n - 1);
}
}
In the example above, the documenting comment provides a description of the factorial function, including the parameter type and return type. This information can be used to generate documentation or provide additional context for other developers working on the codebase.
Conditional Comments
Conditional comments are a special type of comment that are only recognized by certain versions of Internet Explorer (IE). They allow developers to write code specifically for different versions of IE or to exclude code from specific versions. However, it’s important to note that conditional comments are deprecated and should not be used in modern web development.
Example:
<!--[if IE]>
<p>This content is only displayed in Internet Explorer.</p>
<![endif]-->
In the example above, the conditional comment is used to display a specific message only in Internet Explorer.
Conclusion
JavaScript comments are an invaluable tool for developers to improve code readability, provide explanations, and temporarily disable code sections. By using single-line comments, multi-line comments, documenting comments, or conditional comments, developers can enhance the clarity and maintainability of their code.