Basic syntax and comments — Introduction to JavaScript

Basic syntax

A JavaScript program is a list of statements (instructions) that the engine executes from top to bottom, one after another.

Each statement can end with ;. JavaScript sometimes inserts it for you, but getting into the habit of adding it prevents subtle bugs:

let age = 30;
console.log(age);

Comments are text that the engine ignores. They're used to explain the code to other people (and to your future self!):

// This is a single-line comment

/*
  This is a comment
  spanning multiple lines
*/

JavaScript is case-sensitive: age, Age, and AGE are three different names.

Comments and multiple statements

// Calculate the area of a rectangle
let base = 5;
let height = 3;
let area = base * height; // base times height
console.log("The area is", area);