Master primitive types (number, string, boolean), reference types (objects, arrays), and type coercion. Understanding the distinction between mutable and immutable values is critical for avoiding bugs.

• Primitive types (number, string, boolean)
• Reference types (objects, arrays)
• Type coercion

const greeting = 'Hello';
let count = 42;
var active = true;
const person = { name: 'Alice', age: 30 };
const numbers = [1, 2, 3, 4, 5];
console.log(typeof greeting); // string
console.log(typeof count); // number
console.log(typeof active); // boolean

• Variables are declared correctly
• Objects and arrays are reference types

• Use const by default, let for variables that change, avoid var
• Remember: typeof null === 'object' is a known JavaScript quirk
• Objects and arrays are reference types—modifying them affects the original

Master primitive types (number, string, boolean), reference types (objects, arrays), and type coercion. Understanding the distinction between mutable and immutable values is critical for avoiding bugs.

• Primitive types (number, string, boolean)
• Reference types (objects, arrays)
• Type coercion

const greeting = 'Hello';
let count = 42;
var active = true;
const person = { name: 'Alice', age: 30 };
const numbers = [1, 2, 3, 4, 5];
console.log(typeof greeting); // string
console.log(typeof count); // number
console.log(typeof active); // boolean

• Variables are declared correctly
• Objects and arrays are reference types

• Use const by default, let for variables that change, avoid var
• Remember: typeof null === 'object' is a known JavaScript quirk
• Objects and arrays are reference types—modifying them affects the original