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How To Pick And Omit Keys in TypeScript?

How to Declare Specific Type of Keys in an Object in TypeScript ?

Last Updated : 20 Aug, 2024

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In TypeScript, object definitions can include specific key-value types using index signatures. You can declare specific types of keys in an object by using different methods as listed below:

Table of Content

Using Mapped Types
Using Interface
Using Inline Mapped Types with type
Using Record Utility Type

Using Mapped Types

You can define your mapped type using the type alias in TypeScript that can be used to specify the keys of a particular type in an object.

Syntax:

type customType = {};

Example: The below code explains the use of the mapped types to declare specific type keys in an object.

JavaScript

type MyObject = { [key: string]: number; }; const obj: MyObject = { a: 1, b: 2, c: 3 }; console.log(obj);

Output:

{ a: 1, b: 2, c: 3 }

Using Interface

You can also use an interface to define your custom type where the keys of the object are typed to a specific type and can later be used to type the interface.

Interface interfaceName{}

Example: The below code example explains the use of the interface to declare specific type of keys in an object.

JavaScript

interface MyObject {     [key: string]: number; }  const obj: MyObject = {     a: 1,     b: 2,     c: 3 };  console.log(obj);

Output:

{ a: 1, b: 2, c: 3 }

Using Inline Mapped Types with type

You can define a mapped type inline using the type keyword in TypeScript. This allows you to specify the keys of a particular type directly within the type declaration.

Syntax:

type TypeName = { [KeyType]: ValueType };

Example: This TypeScript code defines a type MyObject allowing string keys with number values. It creates an object obj with properties assigned numeric values and logs it.

JavaScript

type MyObject = { [key: string]: number }; const obj: MyObject = { a: 1, b: 2, c: 3 }; console.log(obj);

Output:

{   "a": 1,   "b": 2,   "c": 3 }

Using Record Utility Type

TypeScript provides utility types that help in creating complex types from existing ones. These can be particularly useful for specifying specific key types in an object.

Example: The Record utility type is used to construct an object type with specified keys and a uniform value type.

JavaScript

// Define a type with specific keys of a certain type type MyObject = Record<'name' | 'age' | 'email', string>;  // Create an object conforming to the specified type const obj: MyObject = {     name: "Nikunj",     age: "22",     email: "[email protected]" };  console.log(obj);

Output

{ name: 'Nikunj', age: '22', email: '[email protected]' }

In this article, we explored different methods to define specific key-value types in TypeScript using index signatures. We covered using mapped types, interfaces, and inline mapped types with the type keyword. Each method allows for flexible and robust object type definitions, ensuring type safety and consistency within your TypeScript code.

How To Pick And Omit Keys in TypeScript?

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Article Tags :

JavaScript
Web Technologies
TypeScript

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