JavaScript Syntax

JavaScript syntax is the set of rules for how to write JavaScript code.

Statements

Programs are made of statements, which are instructions the computer runs one by one:

js
let x = 5;
let y = 6;
let z = x + y;

Semicolons

Statements often end with a semicolon ;. Semicolons separate statements and make code predictable. Most programmers always use them.

Values

JavaScript has two kinds of values:

• Literals: fixed values like 5 or "Hello"
• Variables: values stored in names, created with let or const

Identifiers

Names for variables, functions, and labels are called identifiers:

• Can contain letters, digits, _, and $
• Must start with a letter, _, or $
• Are case sensitive: x and X are different
• Cannot use reserved words like let or function

Case sensitivity

js
let Name = "Ada";
let name = "Bob";

Name and name are two completely different variables.

Comments

Comments are ignored by JavaScript:

js
// This is a single line comment

/* This is a
   multi-line comment */

TL;DR

• Code is made of statements, usually ending with ;.
• Use let and const to create variables.
• Identifiers start with a letter, underscore, or $.
• JavaScript is case sensitive.
• Use // and / / for comments.