Functional Patterns for Node.js/TypeScript

Overview

Functional programming patterns that promote testability, composability, and maintainability.

Pure Functions

Definition

A pure function:

• Always returns the same output for the same input
• Has no side effects (no I/O, no mutation)

Examples

// Pure: Deterministic, no side effects
const add = (a: number, b: number): number => a + b;