Make some of the Properties in a type Optional in TypeScript

Make some of the Properties in a type Optional in TypeScript #

To make some of the properties in a type optional, create a utility type that takes a type and one or more property names as parameters and constructs a new type with the specified properties marked as optional.

index.ts

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interface Employee {
  id: number;
  name: string;
  salary: number;
}

type MakeOptional<Type, Key extends keyof Type> = Omit<Type, Key> &
  Partial<Pick<Type, Key>>;

// 👇️ make id optional
type T1 = MakeOptional<Employee, 'id'>;

const emp1: T1 = {
  name: 'Alice',
  salary: 100,
};

// 👇️ make id and name optional
type T2 = MakeOptional<Employee, 'id' | 'name'>;

const emp2: T2 = {
  salary: 200,
};

The MakeOptional utility type takes a type and one or more of its property names as parameters and returns a new type with the specified properties marked as optional.

We used the Omit utility type to construct a new type by picking all of the properties from the provided type and removing the specified keys.

index.ts

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interface Employee {
  id: number;
  name: string;
  salary: number;
}

// 👇️ type O1 = {
//     name: string;
//     salary: number;
// }
type O1 = Omit<Employee, 'id'>;

// 👇️ type O2 = {
//     salary: number;
// }
type O2 = Omit<Employee, 'id' | 'name'>;

Notice that we can specify more than one property name by separating them with a pipe | symbol (called union type).

Now that we have a type with the specified properties removed, we use the Pick utility type to construct a type consisting only of the specified properties and mark them as optional via the Partial utility type.

index.ts

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interface Employee {
  id: number;
  name: string;
  salary: number;
}

// 👇️ type P1 = {
//     id: number;
// }
type P1 = Pick<Employee, 'id'>;

// 👇️ type P2 = {
//     id: number;
//     name: string;
// }
type P2 = Pick<Employee, 'id' | 'name'>;

The Partial utility type is used to construct a new type with all of the properties of the provided type set to optional.

Here is the entire code snippet.

index.ts

Copied!
interface Employee {
  id: number;
  name: string;
  salary: number;
}

type MakeOptional<Type, Key extends keyof Type> = Omit<Type, Key> &
  Partial<Pick<Type, Key>>;


// 👇️ make `id` optional
type T1 = MakeOptional<Employee, 'id'>;

const emp1: T1 = {
  name: 'Alice',
  salary: 100,
};

// 👇️ make id and name optional
type T2 = MakeOptional<Employee, 'id' | 'name'>;

const emp2: T2 = {
  salary: 200,
};

In short, the Omit<Type,Key> part gets us a type that excludes all of the specified properties.

The Pick<Type,Key> syntax gets us a type that consists only of the specified properties.

The Partial<> utility type makes the specified properties optional.

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Make some of the Properties in a type Optional in TypeScript

Make some of the Properties in a type Optional in TypeScript #

Borislav Hadzhiev