Comments in JavaScript are lines of code that are ignored by the JavaScript engine. They are used to explain and clarify the code, making it easier to understand and maintain. Comments can also be used to temporarily disable code during development and debugging. There are two types of comments in JavaScript: single-line comments and multi-line comments.

  1. Single-line Comments Single-line comments start with two forward slashes (//). Everything following // on that line will be ignored by the JavaScript engine.

    Example:

      // This is a single-line comment
let x = 10; // This is another single-line comment

  2. Multi-line Comments Multi-line comments start with /* and end with /. They can span multiple lines and everything between / and */ will be ignored by the JavaScript engine.

    Example:

      /*
This is a multi-line comment.
It can span multiple lines.
*/
let y = 20;

Best Practices for Using Comments

  1. Explain the Code: Use comments to explain complex logic or algorithms. Avoid stating the obvious, but provide context where necessary.

      // Calculate the area of a circle
let radius = 5;
let area = Math.PI * radius ** 2; // πr²

  2. Comment Out Code: Temporarily disable code that you don’t want to execute without deleting it. This is useful for debugging.

      // let z = 30;
// console.log(z);

  3. Header Comments: Use header comments to describe the purpose of the file or function, including any important information like parameters and return values.

      /**
 * Calculate the factorial of a number
 * @param {number} n - The number to calculate the factorial of
 * @returns {number} - The factorial of the input number
 */
function factorial(n) {
    if (n === 0) {
        return 1;
    }
    return n * factorial(n - 1);
}

  4. TODO Comments: Use TODO comments to mark areas of the code that need further development or review.

      // TODO: Optimize this function for better performance
function heavyComputation() {
    // ...
}