TypeScript Type Aliases

Type aliases are a powerful feature in TypeScript that allow developers to create custom names for any type. They provide a way to simplify complex type definitions and enhance code readability.

What are Type Aliases?

Type aliases create a new name for a type. They don't create a new type; instead, they give a name to an existing type. This can be particularly useful when working with complex types or when you want to create a more descriptive name for a type.

Syntax

To create a type alias, use the type keyword followed by the alias name and the type definition:

type AliasName = TypeDefinition;

Examples

1. Simple Type Alias

type UserID = number;

let userId: UserID = 123456;

2. Complex Type Alias

type Point = {
    x: number;
    y: number;
};

let coordinate: Point = { x: 10, y: 20 };

Use Cases

• Simplifying complex types
• Creating more descriptive names for types
• Improving code readability
• Reducing code duplication

Type Aliases vs Interfaces

While type aliases and interfaces can be used interchangeably in many cases, there are some differences:

Type Aliases	Interfaces
Can represent primitives, unions, and tuples	Can only represent object shapes and function signatures
Cannot be extended or implemented	Can be extended and implemented

Best Practices

• Use descriptive names for type aliases
• Prefer interfaces for public API definitions
• Use type aliases for complex types or unions
• Combine with union types and intersection types for more flexibility

Advanced Usage

Type aliases can be combined with other TypeScript features for more advanced type definitions:

type StringOrNumber = string | number;
type Callback = (data: string) => void;
type PointWithLabel = Point & { label: string };

By mastering type aliases, you can create more expressive and maintainable TypeScript code. They are an essential tool in a TypeScript developer's toolkit, working alongside other features like generics and conditional types.