The Valof Book

v0.8.2

Write robust domain logic in TypeScript
just by following the conventions.

The Valof Book is both a guide and a reference. Read it in order to learn the conventions, or use the sidebar to find a specific topic.

Important

Valof is pre-1.0. A minor release can change the API.

Why Valof?

Valof is an opinionated value-object helper for TypeScript that enforces the conventions through types and linting.

• Nominal-ish typing with a phantom brand: TypeScript distinguishes one Val type from another, with nothing to pay at runtime.

• Values as plain data: Vals stay objects, arrays and primitives. They serialize without adapters and fit directly into React and other framework state. No classes, no prototypes.

• Immutability: Vals are immutable. Their types are deeply readonly, and their constructors copy their inputs, so an original reference cannot mutate them.

• No as casts in your code: Valof owns the cast required to construct a branded value.

• Companion object: Keep a type’s constructor and functions together without a class. The first Val parameter is inferred.

• “Parse, don’t validate”: Every creation and derivation goes through one seal. Use any validation library and any Result type.

• Copy only what changes: patch copies only the paths it changes. Untouched branches keep their reference identity.

• Rust-like abstractions (experimental): Enum is a closed set of variants with exhaustive match. Trait shares behavior across Vals. dyn adds dynamic dispatch without classes, holding different types together.

• Built-in linter: Catch convention violations through ESLint, Oxlint or the standalone command.

• Lightweight: Starts from 852 B gzipped, with no runtime dependencies.

For background on individual features, see TypeScript problems Valof addresses.