Working with Partial Types in TypeScript

Working with Partial Types in TypeScript

Partial types are a great way to create reusable, extensible types in TypeScript. They allow us to define a type that is both incomplete and dynamic. A partial type is usually created when we don't know all the properties that will be used at compile time, or when we want to use a subset of properties from an existing type.

For instance, let's say we have a type for a user in our system, called User, which looks like this:

interface User {
  name: string;
  age: number;
  address: string;
}

We can create a partial type for this type by using the keyword partial:

type PartialUser = partial;

With this type, we can create a variable that has any combination of the properties in the User type:

let myUser: PartialUser = {
  name: 'John Doe',
  age: 42
};

Partial types are must useful when you need to perform some kind of partial "mapping" from one type to another. For instance, if we want to create a type that contains only the name and age properties from our User type, we could do so like this:

type UserNameAndAge = partial<User, {name: string, age: number}>;

let myUser: UserNameAndAge = {
  name: 'John Doe',
  age: 42
};

This is a powerful feature that can be used to create reusable, extensible types. If you're building an application in TypeScript, you should definitely consider using partial types to help you write better, more maintainable code.