Custom UUID Scalar for GraphQL on NestJS. Remember to properly set our "custom" type → https://docs.nestjs.com/graphql/resolvers#args-decorator-options

uuid.class-validator.scalar.ts

// Modified "vanilla" example. It uses the `isUUID()` function from the `class-validator` package.

import { isUUID } from 'class-validator';
import { GraphQLScalarType, StringValueNode } from 'graphql';

function validate(uuid: unknown): string | never {
  if (!isUUID(uuid)) {
    throw new Error('The given value is not a UUID string.');
  }
  return uuid as string;
}

export const UuidScalar = new GraphQLScalarType({
  name: 'UUID',
  description: 'Universally Unique Identifier (UUID). Example: `123e4567-e89b-12d3-a456-426614174000`.',
  serialize: (value) => validate(value),
  parseValue: (value) => validate(value),
  parseLiteral: (ast: StringValueNode) => validate(ast.value),
});

uuid.vanilla.scalar.ts

// Source: https://docs.nestjs.com/graphql/scalars#create-a-custom-scalar

import { GraphQLScalarType, StringValueNode } from 'graphql';

const regex = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;

function validate(uuid: unknown): string | never {
  if (typeof uuid !== 'string' || !regex.test(uuid)) {
    throw new Error('Invalid UUID');
  }
  return uuid;
}

export const UuidScalar = new GraphQLScalarType({
  name: 'UUID',
  description: 'Universally Unique Identifier (UUID). Example: `123e4567-e89b-12d3-a456-426614174000`.',
  serialize: (value) => validate(value),
  parseValue: (value) => validate(value),
  parseLiteral: (ast: StringValueNode) => validate(ast.value),
});