An Introduction to Functional Programming in JavaScript

Functional programming is a long‑standing programming paradigm whose roots lie in the λ‑calculus that predates modern computers. This article provides a rapid overview of its history, basic techniques, key characteristics, and practical guidelines, using JavaScript as the illustrative language.

The content covers:

Definition and origins of functional programming, including λ‑calculus and its substitution and reduction rules.

JavaScript’s arrow functions as λ‑expressions, and how they differ from traditional function declarations.

Fundamental concepts such as function arity, currying, point‑free style, and higher‑order functions.

Practical examples of code composition, reuse, and the use of utilities like curry, compose, pipe, and map.

Key functional programming properties: first‑class functions, pure functions, referential transparency, immutability, lazy evaluation, and type inference.

Discussion of closures, partial application, and how these ideas map to real‑world JavaScript development.

The article also compares functional programming with object‑oriented approaches, highlights advantages and drawbacks, and points to further reading on applying functional concepts in frameworks such as Redux/React.