ELab Team

Dec 8, 2021 · Frontend Development

Understanding Covariance, Contravariance, and Bivariance in TypeScript

This article explains TypeScript's covariant, contravariant, bivariant, and invariant type relationships, why methods and function properties behave differently under strictFunctionTypes, how ESLint's @typescript-eslint/method-signature-style rule enforces function property signatures, and practical ways to achieve safer type definitions.