What data types exist in JavaScript? How do primitives differ from objects? How are they stored in memory?

In JavaScript, the following data types exist:

Primitives:

• Number
• String
• Boolean
• Null
• Undefined
• Symbol
• BigInt

Objects:

• Object
• Array
• Function
• Date, RegExp, and other built-in objects

Differences between primitives and objects:

• Primitives are stored directly in the stack and are passed by value.
• Objects are stored in the heap, and the variable contains a reference to the object.
• Primitives are immutable, objects are mutable.

Memory storage:

• Primitives occupy a fixed space and are quickly accessible.
• Objects are stored in the heap, and variables contain pointers to them.

For example:

let a = 5;       // a stores the value 5
let b = a;       // copy of the value
b = 10;          // a will not change

let obj1 = {x:1};
let obj2 = obj1;  // obj2 and obj1 refer to the same object
obj2.x = 2;      // obj1.x will also change

Thus, primitives are simple values, and objects are complex structures with reference semantics.