What data types are there in JavaScript? What are the major groups and how do they differ?

In JavaScript, there are two main data types: primitives and objects.

Primitive types:

• undefined — the default value for undeclared variables.
• null — a special value indicating the absence of a value.
• boolean — logical values true or false.
• number — numbers (integers and floating-point).
• bigint — integers of arbitrary length.
• string — sequences of text.
• symbol — unique and immutable identifiers.

Objects:

• Complex data structures that can contain properties and methods.
• Include arrays, functions, dates, regular expressions, and user-defined objects.

The difference is that primitives are stored and passed by value, while objects are by reference. Primitives are immutable, objects are mutable.

Example:

let a = 5; // number
let b = 'hello'; // string
let c = { name: 'John' }; // object

// Primitives are copied by value
let d = a;
 d = 10; // a remains 5

// Objects are copied by reference
let e = c;
 e.name = 'Jane'; // c.name also changes to 'Jane'