JS Syntax

JavaScript Syntax: Rules, Literals, & Identifiers

JavaScript syntax defines the set of rules for structuring valid code. JavaScript is case-sensitive, uses the Unicode character set, and distinguishes between fixed values (literals) and variable storage containers (variables).

Key Syntax Rules Overview

flowchart TD
    Syntax["JavaScript Syntax Rules"] --> Case["Case Sensitivity: myVar !== myvar"]
    Syntax --> Ident["Identifiers: Must start with Letter, $, or _"]
    Syntax --> Literals["Literals: Fixed values (42, 'Hello', true, {id: 1})"]
    Syntax --> Keywords["Reserved Keywords: let, const, function, class"]

Identifier Naming Rules

Practical Code Example

// Syntax Demo: Literals, Identifiers, and Case Sensitivity

// Fixed Literals
const NUMBER_LITERAL = 100.50;
const STRING_LITERAL = "KodSolution Tutorial";
const BOOLEAN_LITERAL = true;
const ARRAY_LITERAL = ["HTML", "CSS", "JavaScript"];
const OBJECT_LITERAL = { domain: "kodersolution.com", status: 200 };

// Identifier Case Sensitivity Demonstration
let userScore = 95;
let UserScore = 40; // Completely distinct variable from userScore

console.log(`userScore: ${userScore}, UserScore: ${UserScore}`);

// Valid Identifier Characters (Letters, $, _)
let $element = document.querySelector("#app"); // Valid prefix $
let _internalState = "idle";                   // Valid prefix _
let user10 = "Valid numeric suffix";           // Numbers allowed after first char

console.log(`State: ${_internalState}, Tag: ${user10}`);

Best Practices & Gotchas

• Strict Case Sensitivity: myFunction and myfunction refer to two completely different memory locations.
• Do Not Start Identifiers with Digits: let 1stUser = "Alex" will trigger a SyntaxError.
• Use Descriptive Names: Prefer isEmailValidated over vague variables like chk.

Self-Check Challenge

Which of the following identifier names are invalid in JavaScript?

1. _userStatus
2. 2ndPlace
3. $accountBalance
4. user-name