io-ts

import * as t from 'io-ts'; import { pipe } from 'fp-ts/function'; import * as E from 'fp-ts/Either'; import { PathReporter } from 'io-ts/PathReporter'; // 1. Define a runtime type using io-ts codecs const User = t.type({ id: t.number, name: t.string, email: t.string, isAdmin: t.boolean, tags: t.array(t.string), }); // Infer the TypeScript type from the runtime type type User = t.TypeOf<typeof User>; // 2. Data to decode const validUserData = { id: 123, name: 'Alice', email: 'alice@example.com', isAdmin: false, tags: ['developer', 'typescript'], }; const invalidUserData = { id: 'abc', // Invalid type name: 'Bob', email: 'bob@example.com', isAdmin: 'no', // Invalid type tags: [123, 'tester'], // Mixed types }; // 3. Decode valid data pipe( User.decode(validUserData), E.fold( (errors) => console.error('Failed to decode valid data:', PathReporter.report(E.left(errors))), (user) => { console.log('Successfully decoded valid user:', user); const _user: User = user; // Type-check confirms 'user' is of type User console.log('Is Alice an admin?', _user.isAdmin); } ) ); // 4. Decode invalid data and report errors pipe( User.decode(invalidUserData), E.fold( (errors) => console.error('Failed to decode invalid data:', PathReporter.report(E.left(errors))), (user) => console.log('Unexpectedly decoded invalid user:', user) ) ); // Example with a nullable/optional field const OptionalUser = t.partial({ phone: t.string, }); const UserWithOptionalPhone = t.intersection([User, OptionalUser]); const userWithPhone = { id: 456, name: 'Charlie', email: 'charlie@example.com', isAdmin: true, tags: ['lead'], phone: '555-1234' }; pipe( UserWithOptionalPhone.decode(userWithPhone), E.fold( (errors) => console.log('Failed to decode user with phone:', PathReporter.report(E.left(errors))), (user) => console.log('Decoded user with phone:', user) ) );