Make all properties Optional except one in TypeScript

Make all properties Optional except one in TypeScript #

To make all of the properties of a type optional except one, use an interface to extend the type passing it to the Partial utility type, e.g. interface OptionalExceptSalary extends Partial<Employee> {} and override the specific property setting it to required.

index.ts

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

interface OptionalExceptSalary extends Partial<Employee> {
  salary: number;
}

const emp: OptionalExceptSalary = {
  salary: 100,
};

We used the Partial utility type to construct a type where all of the properties are set to optional.

index.ts

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

// 👇️ type Opt = {
//     id?: number | undefined;
//     name?: string | undefined;
//     salary?: number | undefined;
// }
type Opt = Partial<Employee>;

The only properties we want to override in the new interface are the ones we want to mark as required.

You can achieve the same result by using a type alias.

index.ts

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

type OptionalExceptSalary = Partial<Employee> & {
  salary: number;
};

const emp: OptionalExceptSalary = {
  salary: 100,
};

You can use this approach to mark all properties except N as optional.

An alternative approach is to create a utility type that makes the specified properties 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<Type>;

// 👇️ mark salary as optional
const emp: MakeOptional<Employee, 'salary'> = {
  id: 1,
  name: 'James',
};

The MakeOptional utility types takes a type and one of the type's keys as parameters and marks the specified key as optional (salary in the example).

You don't have to only mark a single property 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<Type>;


// 👇️ mark salary and name as optional
const emp: MakeOptional<Employee, 'salary' | 'name'> = {
  id: 1,
};

The Omit utility constructs a new type by picking all 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 T = {
//     id: number;
//     name: string;
// }
type T1 = Omit<Employee, 'salary'>;

// 👇️ type T2 = {
//     id: number;
// }
type T2 = Omit<Employee, 'salary' | 'name'>;

The first example look something like:

index.ts

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

// 👇️ type T10 = {
//     id: number;
//     name: string;
// } & Partial<Employee>
type T10 = { id: number; name: string } & Partial<Employee>;

// 👇️ only salary is marked as optional
const example: T10 = {
  id: 1,
  name: 'James',
};

Make all properties Optional except one in TypeScript

Make all properties Optional except one in TypeScript #

Borislav Hadzhiev