type-fest — Essential TypeScript Utility Types Collection

Introduction

type-fest provides a curated, well-tested collection of TypeScript utility types that fill gaps in the built-in utility types. Maintained by Sindre Sorhus, it covers deep partial, readonly, JSON types, string manipulation, and dozens more patterns commonly needed across TypeScript projects.

What type-fest Does

• Provides deep recursive versions of built-in types like PartialDeep and ReadonlyDeep
• Offers strict variants of Extract, Exclude, and Omit that catch typos at compile time
• Includes JSON-related types for parsing and serialization safety (JsonValue, JsonObject)
• Supplies string literal manipulation types like CamelCase, KebabCase, and Split
• Adds array utilities like FixedLengthArray, ArraySlice, and LastArrayElement

Architecture Overview

type-fest is a pure type-level library with zero runtime code. Each type is defined in its own source file, tree-shakeable by design. The library requires TypeScript 5.9 or later and strict mode enabled. Types are organized by category and exported from a single entry point for convenient imports.

Self-Hosting & Configuration

• Install via npm: npm install type-fest
• Import types using import type syntax only (no runtime footprint)
• Requires strict: true in tsconfig.json
• Requires TypeScript 5.1 or later (5.9 recommended for latest features)
• Works with any bundler or runtime since it emits no JavaScript

Key Features

• Over 200 carefully designed utility types
• Zero runtime overhead since every export is a pure type
• Strict mode variants that enforce exact key matching
• Extensive JSDoc documentation with inline examples for every type
• Battle-tested across thousands of npm packages

Comparison with Similar Tools

• ts-toolbelt — larger library with 300+ types; heavier, more complex API surface
• utility-types — smaller collection focused on mapped and conditional types; less maintained
• ts-essentials — overlapping scope with deep partial and readonly types; fewer string utilities
• TypeScript built-in utilities — Partial, Pick, Omit, etc.; lacks deep variants and string types
• simplytyped — lightweight alternative; discontinued

FAQ

Q: Does type-fest add any runtime code to my bundle? A: No. Every export is a TypeScript type, removed entirely during compilation.

Q: Which TypeScript version is required? A: TypeScript 5.1 or later with strict mode enabled. Some newer types require 5.9.

Q: Can I use individual types without importing the whole package? A: Yes. Use import type { CamelCase } from 'type-fest' and your bundler will include only the type reference, which compiles away.

Q: How is PartialDeep different from the built-in Partial? A: The built-in Partial only makes top-level properties optional. PartialDeep recursively makes every nested property optional as well.

Sources

• https://github.com/sindresorhus/type-fest
• https://www.npmjs.com/package/type-fest