TypeScript Aliases Type (original) (raw)

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 <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mrow><mi>s</mi><mi>h</mi><mi>a</mi><mi>p</mi><mi>e</mi></mrow><mi>a</mi><mi>t</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">{shape} at (</annotation></semantics></math>shapeat({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: "akshit.saxena@geeksforgeeks.com", 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 akshit.saxena@geeksforgeeks.com.

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.