Type aliases and interfaces are used to define custom types in TypeScript. While they share many similarities, they differ in features such as declaration merging, type composition, and supported use cases.
- Type Aliases are suitable for unions, tuples, primitive types, function types, and object types.
- Interfaces are primarily designed for defining object shapes and support extension and declaration merging.
Type Aliases vs Interfaces
Here are some differences:
Type Aliases | Interfaces Type |
|---|---|
Declared using the type keyword. | Declared using the interface keyword. |
Can define primitives, objects, unions, intersections, tuples, and function types. | Primarily defines the structure of objects and callable types. |
Uses the & operator to combine multiple types. | Uses the extends keyword to inherit from other interfaces. |
Does not support declaration merging. | Supports declaration merging. |
Can be implemented by classes if it represents an object type. | Can be implemented by classes using the implements keyword. |
Supports union types (|). | Does not directly support union types. |
Supports tuple types. | Does not directly support tuple types. |
Best suited for unions, tuples, function types, and complex type compositions. | Best suited for defining object structures, APIs, and class contracts. |
