ArrayThat

ArrayThat is a lightweight, pure‑functional array manipulation library for JavaScript and TypeScript. It was first released in 2018 by developer Alex Nguyen under an MIT license. The library was created to provide a concise, chainable API for common operations such as filtering, mapping, grouping, and pagination while maintaining full type safety. Its API is intentionally minimal: every function returns a new array instead of mutating the original, making it well suited for use in Redux reducers and React state updates.

The core of ArrayThat centers around the ArrayThat class, which wraps a native JavaScript array and exposes a fluent interface. Typical usage follows the pattern: `ArrayThat.from([1, 2, 3, 4]).filter(x => x % 2).map(x => x * 10).toArray()`. The library also includes utility functions for chunking, flattening deeply nested arrays, and computing statistical metrics such as mean, median, and variance of numerical data. A small set of built‑in error checks alerts developers to null or undefined entries while preserving performant operation on large datasets.

The project is actively maintained on GitHub, with release 1.4.0 adding safe optional chaining for nested arrays. Community contributors have added language bindings for Rust and Python, making the core functionality available in server‑side code and command‑line utilities. Documentation is available through a generated API reference and tutorial on the official site. The library is considered stable for production use in both browser and Node.js environments.