JavaScript Comments


Introduction

When working with JavaScript, it's important to make your code easy to understand and maintain. One way to do this is by using comments. Comments are lines of code that are ignored by the browser. They are used to explain what the code does and why it was written that way.

Single Line Comments

Single line comments are denoted by two forward slashes (//). Anything that follows on the same line will be ignored by the browser. Single line comments are useful for explaining short snippets of code. For example:

// This is a single line comment

var x = 5; // This variable is used to store a number

Single line comments can also be used to disable a line of code. This can be useful when you want to test different parts of your code without deleting anything. For example:

// var x = 5; // This line of code is currently disabled

var y = 10;

var sum = x + y; // This line will throw an error because x is not defined

Single line comments can also be used to add context to your code. For example:

var age = 18;
// The legal voting age is 18
if (age >= 18) {
  console.log("You are eligible to vote");
}

Single line comments can also be used to provide instructions for other developers who might be working on the same code. For example:

// TODO: Refactor this code to use a loop
var numbers = [1, 2, 3, 4, 5];
var sum = 0;
for (var i = 0; i < numbers.length; i++) {
  sum += numbers[i];
}

Multi-Line Comments

Multi-line comments are denoted by /* and */. Anything between these two symbols will be ignored by the browser. Multi-line comments are useful for explaining larger blocks of code. For example:

/* This is a multi-line comment
   It can span over multiple lines
   This code is used to calculate the sum of two numbers */
var x = 5;
var y = 10;
var sum = x + y;

Multi-line comments can also be used to temporarily disable a block of code. This can be useful when you want to test different parts of your code without deleting anything. For example:

/*
var x = 5;
var y = 10;
var sum = x + y;
*/ // This block of code is currently disabled

var z = 15;
var total = sum + z; // This line will throw an error because sum is not defined

Multi-line comments can also be used to provide documentation for your code. This is especially useful when working on a larger project with multiple developers. For example:

/*
Function: calculateSum

Description:
This function takes two numbers as input and returns their sum.

Parameters:
- x (number): The first number to be added.
- y (number): The second number to be added.

Returns:
The sum of x and y.

Example:
calculateSum(5, 10); // Returns 15
*/
function calculateSum(x, y) {
  return x + y;
}

Multi-line comments can be used to provide additional information about your code that might not be immediately obvious. For example, you could use a multi-line comment to explain why a particular algorithm was chosen over another, or to provide a brief history of how the code has evolved over time.

Commenting Best Practices

Here are some best practices to follow when using comments in your JavaScript code:

  • Use comments to explain what the code does, not how it does it. The code should be self-explanatory, and comments should be used to clarify anything that might not be immediately obvious.
  • Keep your comments up to date as you make changes to your code. Outdated comments can be worse than no comments at all.
  • Don't overuse comments - only add them when necessary. Too many comments can make your code harder to read.
  • Use clear and concise language. Your comments should be easy to understand and free of unnecessary jargon.
  • Use consistent formatting throughout your code. This makes it easier to read and understand.

Comments are an important part of writing clean and maintainable JavaScript code. Single line comments are used for short explanations and multi-line comments are used for larger blocks of code. By following best practices, you can ensure that your comments are useful and make your code easier to understand. Remember, the goal of comments is to make your code more readable, so don't be afraid to use them when necessary!

Additional Resources