Welcome to Type-Fest

Type-Fest is a collection of essential TypeScript type utilities that help developers with typing, ensuring a more robust and error-free coding experience. In this guide, we will introduce you to dozens of important APIs provided by Type-Fest, including practical code snippets to illustrate their usage and a sample application that leverages these utilities.

Key Type-Fest Utilities

Let’s dive into some of the most useful Type-Fest API examples:

1. PartialDeep

Make all properties in T deeply optional:

import {PartialDeep} from 'type-fest';

interface User {
  id: number;
  name: string;
  address: {
    street: string;
    city: string;
  };
}

const updateUser: PartialDeep = {
  address: {
    city: 'New York'
  }
};

2. Omit

Omit specific keys from a type:

import {Omit} from 'type-fest';

interface User {
  id: number;
  password: string;
  name: string;
}

type UserWithoutPassword = Omit;

3. Merge

Merge two types into a new type:

import {Merge} from 'type-fest';

interface User {
  id: number;
  name: string;
}

interface Admin {
  role: string;
}

type AdminUser = Merge;
// {id: number; name: string; role: string;}

4. Mutable

Convert readonly properties to mutable:

import {Mutable} from 'type-fest';

interface ReadOnlyUser {
  readonly id: number;
  readonly name: string;
}

type WriteableUser = Mutable;

5. Jsonify

Transform a type to one that is JSON serializable:

import {Jsonify} from 'type-fest';

interface User {
  id: number;
  name: string;
  address: {
    street: string;
    city: string;
  };
}

type JsonUser = Jsonify;
// {id: number; name: string; address: {street: string; city: string;};}

Sample Application

Let’s create a simple app using some of the Type-Fest utilities shown above:

// Import Type-Fest utilities
import {Merge, PartialDeep, Jsonify} from 'type-fest';

// Interfaces
interface User {
  id: number;
  name: string;
  address: {
    street: string;
    city: string;
  };
}

interface Admin {
  role: string;
}

// Create a type for a user update
const updateUser: PartialDeep = {
  address: {
    city: 'San Francisco'
  }
};

// Merge User and Admin to create an AdminUser type
type AdminUser = Merge;

const adminUser: AdminUser = {
  id: 1,
  name: 'Alice',
  role: 'Administrator',
  address: {
    street: 'Market St',
    city: 'San Francisco'
  }
};

console.log('Updated User:', updateUser);
console.log('Admin User:', adminUser);

// Creating a JSON serializable user type
type JsonUser = Jsonify;

const jsonUser: JsonUser = JSON.parse(JSON.stringify(adminUser));
console.log('JSON User:', jsonUser);

With Type-Fest, managing complex type operations in TypeScript becomes easier and more efficient. These utilities not only make your code cleaner but also greatly reduce potential errors.

Happy coding!

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