What is the difference between functional programming and object-oriented programming?

Question

Accepted Answer

**FP** — pure functions, immutability. **OOP** — objects, state.

**Functional Programming:**
- Pure functions (no side effects).
- Immutability.
- Higher-order functions.
- Declarative.

```
FP:
const add = (a, b) => a + b;
const double = x => x * 2;
[1,2,3].map(double).filter(x => x > 2);
(Pure functions, no side effects)
```

**Object-Oriented Programming:**
- Objects with state.
- Encapsulation.
- Inheritance.
- Imperative.

```
OOP:
class User {
  constructor(name) { this.name = name; }
  getName() { return this.name; }
}
(Objects with state)
```

**Key differences:**
- **FP** — functions.
- **OOP** — objects.
- **FP** — immutable.
- **OOP** — mutable state.

Systems Analyst: What is the difference between functional programming and object-oriented programming?