How Category Theory Concepts Map to Functional Programming in JavaScript

A technical explainer outlines how category theory — the mathematics of composition — underpins functional programming primitives in JavaScript. Although JavaScript is not a purely functional language, its support for first-class functions makes it possible to implement core constructs such as Functors, Monoids, and Monads. A Functor wraps a value in a container and exposes a map method, allowing chained transformations without extracting the value. Monoids provide an identity value and an associative combining operation, forming the basis of list reduction via Array.prototype.reduce. Monads extend Functors with a flatMap or chain method that prevents nested containers when functions themselves return wrapped values.