JavaScript Comments

Comments are notes you write inside your code. JavaScript skips them completely — they exist for human readers.

Single-line Comments

Everything after // on the same line is a comment.

// This is a single-line comment.
let total = 0; // Comments can also follow code on the same line.
console.log(total);

Multi-line Comments

Wrap multi-line notes in /* … */.

/*
  This is a multi-line comment.
  Useful for longer explanations
  or for temporarily disabling
  several lines at once.
*/
let price = 9.99;
console.log(price);

Commenting Out Code

A handy trick while debugging: stick a // in front of a line to disable it without deleting it.

let count = 10;
count = count + 1;
// count = count * 2;   ← temporarily disabled
console.log(count);     // 11

When to Comment

Good code uses clear names so the what is obvious. That leaves comments for the why: a constraint, a workaround, a non-obvious decision.

A good comment ages well. A comment that explains what the code does becomes a lie the moment someone refactors. A comment that explains why stays true.

Up Next

You’ve seen output, statements, syntax, and comments. Time for the single most useful tool in any programming language: variables.