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Javascript Comments

JavaScript comments are statements in your code that are not executed by the JavaScript engine, but are instead used to add information about your code for humans reading the code.

There are two types of comments in JavaScript:

Single-line comments:​

Single-line comments start with two forward slashes (//) and continue until the end of the line.

As an example:

// This is a single-line comment

Multi-line comments​

Multi-line comments start with / and end with /. They can span across multiple lines.

As an example:

/*
This is a multi-line comment
It can span across multiple lines
*/
Using comments

Comments clarify code, help in code maintenance & help others understand it. It is always a good practice to use them.

Uses of comments​

Commenting out code​

Comments can also be used to prevent execution of code. This is useful when you want to debug your code by preventing a part of the code from executing.

As an example:

function add(a, b) {
  // return a + b;
}

In the above example:

  • The function add() will not return anything.

Code documentation​

Comments can also be used to generate documentation for your code. This is useful when you are writing a library or a framework.

As an example:

/**
 * This function adds two numbers.
 * @param {number} a - The first number
 * @param {number} b - The second number
 * @returns {number} The sum of the two numbers
 */
function add(a, b) {
  return a + b;
}

In the above example:

  • The function add() will return the sum of the two numbers passed to it.
  • The @param tag is used to document the parameters of the function.
  • The @returns tag is used to document the return value of the function.

Comment best practices​

Commenting for readability​

Comments should be used to explain the code. They should not be used to explain what the code does. The code should be self-explanatory.

As an example:

// This function adds two numbers
function add(a, b) {
  return a + b;
}

In the above example:

  • The comment is not required as the function name add() is self-explanatory.

Commenting for future reference​

Comments can be used to add notes and explanations for future reference.

As an example:


// This function adds two numbers
function add(a, b) {
  return a + b;
}

// This function subtracts two numbers
function subtract(a, b) {
  return a - b;
}

In the above example:

  • The comments are not required as the function names add() and subtract() are self-explanatory.