TypeScript Aliases Type

Last Updated : 22 Jan, 2025

In TypeScript, a type alias allows you to assign a custom name to an existing type, enhancing code readability and reusability.

Provide a shorthand for complex types like unions or objects.
Allow naming of primitive types, object types, or functions for clarity.
Simplify repetitive type definitions and improve maintainability.

JavaScript

type Point = {     x: number;     y: number; };  type Shape = "circle" | "square" | "rectangle";  function drawShape(shape: Shape, position: Point): void {     console.log(`Drawing a ${shape} at (${position.x}, ${position.y})`); }  drawShape("circle", { x: 10, y: 20 });

Point is a type alias for an object with x and y as number.
Shape is a type alias for a union of specific string literals.
The drawShape function accepts a Shape and a Point, ensuring strong type safety and clarity.

Output:

Drawing a circle at (10, 20)

Parameters of Type Aliases

AliasName:
- This is the name you assign to the type alias. It must be a valid TypeScript identifier.
- Example: Point, Shape, UserProfile.
ExistingType:
- This refers to the actual data type or structure the alias represents.
- Example: string, number, { x: number; y: number; }.

More Examples of TypeScript aliases Type

Alias for a Union Type

JavaScript

type ID = number | string; let userId: ID; userId = 101; // Valid assignment userId = "A123"; // Also valid

ID is a type alias that allows a variable to be either a number or a string.
This provides flexibility for userId to accept both numeric and alphanumeric identifiers.

Output:

Origin: { x: 0, y: 0 }
Distance from Origin: 0

Defining a User Profile with Type Aliases

JavaScript

type UserProfile = {     username: string;     email: string;     age: number; };  const user: UserProfile = {     username: "Akshit Saxena",     email: "[email protected]",     age: 24, };  function greetUser(profile: UserProfile): string {     return `Hello, ${profile.username}!      You are ${profile.age} years old.      Your email is ${profile.email}.`; }  console.log(greetUser(user));

UserProfile is a type alias for an object with username, email, and age properties.
The greetUser function utilizes this alias to ensure it receives a properly structured user profile.

Output:

Hello, Akshit Saxena! 
    You are 24 years old. 
    Your email is [email protected].

Using Type Aliases for Union Types

JavaScript

type ID = number | string;  function displayId(id: ID): void {     console.log(`The ID is ${id}`); }  displayId(101); displayId("A102");

ID is a type alias representing a union of number and string.
The displayId function accepts an ID, allowing for flexible input types.

Output:

The ID is 101
The ID is A102

Best Practices for Using TypeScript Type Aliases

Use Descriptive Names: Choose clear and meaningful names for type aliases to enhance code readability.
Keep Types Focused: Define type aliases for specific, well-defined structures to maintain clarity.
Document Complex Types: Provide comments or documentation for complex type aliases to aid understanding.