JavaScript Comments

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In JavaScript, comments are used to add notes and explanations to the code. They are ignored by the JavaScript interpreter and do not affect the execution of the code.

Comments are a way for developers to leave notes for themselves and for others who may read the code, explaining how the code works or providing information about specific parts of the code.

There are two types of comments in JavaScript: single-line comments and multi-line comments

Single-line comments:

These comments begin with two forward slashes // and continue until the end of the line. For example:

// This is a single-line comment

Multi-line comments:

These comments begin with a forward slash and an asterisk /* and continue until the closing asterisk and forward slash */.

For example:

/*
This is a 
multi-line comment
*/

Using comments in your JavaScript code is a good practice, as it makes it easier for others to understand and maintain your code.

It's important to keep in mind that, comments are for the developers and not for the users, so it's important to keep the comments clear, concise, and up-to-date.

Examples of comments usage in JavaScript

Here are a few examples of comments in JavaScript:

// Declare a variable x and assign it a value of 5
let x = 5;

// Declare a variable y and assign it a value of 10
let y = 10;

// Declare a function that takes two parameters, a and b
// and returns the sum of a and b
function add(a, b) {
  return a + b;
}

if (x > 0) {  // Check if x is greater than 0
  console.log("x is positive");  // If x is greater than 0, log "x is positive"
} else {
  console.log("x is non-positive");  // If x is not greater than 0, log "x is non-positive"
}

// Use a for loop to log the numbers 0 to 9
for (let i = 0; i < 10; i++) {
  console.log(i); //log the current value of i
}

It's important to notice that placing comments after a line of code can make the code less readable, because the comments will scroll horizontally with the code and make it harder to read. That's why is recommended to place comments before the lines of code or use multi-line comments to explain a section of code.

In addition, comments should be clear, concise, and up-to-date, and not repetitive, just repeating what the code already says. They should provide additional information and context that helps to understand the code better.

Using Comments to Prevent Execution

In JavaScript, comments can also be used to prevent certain lines of code from being executed. This is known as "commenting out" code.

Commenting out code is useful when you want to temporarily remove a line of code from the program without actually deleting it. This allows you to test the program with and without that line of code, without losing the original code.

To comment out a single line of code, you can simply add two forward slashes // at the beginning of the line. For example:

let x = 5;
//let y = 10;

console.log(x);
//console.log(y);

In this example, the line let y = 10; is commented out and the interpreter will ignore it, so the output will be 5.

To comment out multiple lines of code, you can use the multi-line comment notation, which starts with /* and ends with */.

let x = 5;
/*
let y = 10;
let z = 15;
*/
console.log(x);

In this example, the interpreter will ignore all the lines between /* and */, so the output will be 5.