What is the difference between different data types?

In JavaScript, data is divided into primitive types and objects.

Primitive types:

• String: A sequence of characters. Immutable.
• Number: Numbers, including integers and floating-point, as well as Infinity, -Infinity, and NaN.
• Boolean: Logical value (true or false).
• Null: A special value representing the absence of an object.
• Undefined: The value of a variable that has not been assigned a value.
• Symbol: A unique and immutable primitive type used for object property identifiers.
• BigInt: Integers of arbitrary length.

Objects:

• Object: A collection of key-value pairs. Mutable. Examples include arrays, functions, regular expressions, dates.

Main differences:

1. Mutability: Primitive types are immutable, meaning their value cannot be changed directly. Attempting to change them creates a new copy. Objects are mutable; their properties can be added, removed, and modified.
2. Pass by value/reference: Primitive types are passed by value (the value itself is copied). Objects are passed by reference (a reference to the memory location where the object is stored is copied).
3. Comparison: Primitive types are compared by value. Objects are compared by reference (two variables refer to the same object in memory).

// Examples
let str1 = "hello";
let str2 = str1; // str2 gets a copy of the value of str1
str1 = "world"; // A new string "world" is created for str1
console.log(str2); // "hello" - str2 did not change

let obj1 = { name: "Alice" };
let obj2 = obj1; // obj2 gets a reference to the same object as obj1
obj1.name = "Bob"; // The property of the object they both reference is changed
console.log(obj2.name); // "Bob" - obj2 reflects the change

let num1 = 10;
let num2 = 10;
console.log(num1 === num2); // true - values are compared

let objA = { value: 1 };
let objB = { value: 1 };
console.log(objA === objB); // false - references are compared (different objects, even if contents are the same)

Differences table:

Attribute	Primitive types	Objects
Mutability	Immutable	Mutable
Passing	By value	By reference
Comparison	By value	By reference
Storage	Directly in variable	Reference to memory location
Data types	String, Number, Boolean, Null, Undefined, Symbol, BigInt	Object (including arrays, functions, etc.)