type-safe-validator

A validation library designed to take full advantage of the TypeScript type system. All return types are inferred directly from the schema.

Motivation

I wanted a library that would guarantee that my validation schema will always fully comply with my TypeScript interfaces. As far I as know, such a library did not exist.

This library aims to completely stop runtime errors by ensuring that a compiled TypeScript program can never mistakenly receive an invalid object from sources such a REST API.

Benefits

• Less bugs. No disparity between the schema and the interface your code compiles.
• If an object successfully makes its way into your domain, it is guaranteed to be in the correct shape.
• Explicit checks for null and undefined.
• Infinitely nestable schemas for Objects, Tuples, Arrays, Records and Union types.
• Supports literal types.
• Direct support custom parsers and "Opaque" types (see ts-essentials module).
• All excess properties are trimmed and a deep copy is returned. The original object is untouched.

Usage modes

Two primary usages depending on preference:

Use assertValid to get a validated object, or throw if there is an error:

const answer = assertValid(schema, input);

Use getValid to get a tuple which contains a valid object result, or detailed failure information:

const [answer, errors] = getValid(schema, input);

if (answer !== ValidationFail) {
  // Use answer
}

The errors array will contain a list of all error messages, each with a path property, and a human readable message string.

Example

Object schema with different property types, some of which are optional / allow nulls:

interface Schema {
  readonly a: string;
  readonly b: number | null;
  readonly c?: number;
}

const schema = ObjectParser({
  a: StringParser(),
  b: NumberParser({ nullable: true }),
  c: NumberParser({ optional: true })
});

// Mismatch between validation schema and type schema will show as a compile time type error here...
const answer: Schema = assertValid(schema, {
  a: 'foo',
  b: null,
  c: undefined
});

Please see index.spec.ts for more examples.

Inferring a type from the schema

const thing: ParserReturn<typeof schema> = {
  ...
};

Notes

This library is a work in progress however I am already using it in two major projects. Feedback is welcome.