Object Types

Syntax for typing objects.

const vehicle: { maker: string; model: string; year: number } = {
  maker: 'Honda',
  model: 'Civic',
  year: 2008,
};

Infered Type

Type can be Infered.

const vehicle2 = {
  maker: 'Ford',
};
vehicle2.maker = 'Nissan'; // no error
vehicle2.maker = 2; // Error: Type 'number' is not assignable
// to type 'string'.

Optional Properties

Without optional properties.

const vehicle3: { maker: string; mileage: number } = {
  // Error: Property 'mileage' is missing in type
  // '{ type: string; }' but required in type
  // '{ maker: string; mileage: number; }'.
  maker: 'Honda',
};
vehicle3.mileage = 3000;

With optional properties.

const vehicle3: { maker: string; mileage?: number } = {
  // no error
  maker: 'Honda',
};
vehicle3.mileage = 3000;

Index Signatures

const nameAgeMap: { [index: string]: number } = {};
nameAgeMap.Matt = 25; // no error
nameAgeMap.Michael = 'Fifty'; // Error: Type 'string' is not
// assignable to type 'number'.

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