JavaScript is a general-purpose programming language used widely in web browsers and also in server and command-line environments.

Variables and values

Modern JavaScript commonly binds names with const or let:

const name = "Ada";
let count = 3;

const prevents rebinding the name, while let allows reassignment.

Control flow

JavaScript uses braces to delimit blocks:

if (count > 0) {
  console.log("items available");
}

for (const item of items) {
  console.log(item);
}

Functions

Functions can be written in several forms. A function declaration is

function area(width, height) {
  return width * height;
}

Functions are values, so they can also be stored in variables, passed as arguments and returned from other functions.

Arrays and objects

Arrays store ordered values:

const numbers = [2, 4, 6];

Objects group named properties:

const user = { name: "Ada", active: true };

JavaScript supplies a concrete syntax for the same programming foundations as other languages while becoming especially important when code interacts with a web browser.