TypeScript Differences Between Type Aliases and Interfaces Type
In TypeScript, both type aliases and interfaces are used to define custom types, but they have distinct differences and use cases.
- Type Aliases: Allow the definition of types with a custom name, applicable to primitives, unions, tuples, and more complex types.
- Interfaces: Primarily used for defining object types and specifying property names and their types. They can be extended or merged.
Type Aliases
Type aliases in TypeScript allow you to create custom names for types, enhancing code readability and reusability.
type Point = {
x: number;
y: number;
};
function printPoint(point: Point): void {
console.log(`x: ${point.x}, y: ${point.y}`);
}
const myPoint: Point = { x: 10, y: 20 };
printPoint(myPoint);
- The type Point = { x: number; y: number; }; line defines a type alias named Point representing an object with x and y properties, both of which are numbers.
- The printPoint function accepts a parameter of type Point and logs its properties to the console.
- The myPoint constant is declared with the Point type and initialized with appropriate x and y values.
Output:
x: 10, y: 20TypeScript Interfaces
Interfaces in TypeScript define the structure of an object, specifying the required property types and method signatures. They ensure type safety and enhance code clarity.
interface Point {
x: number;
y: number;
}
function displayPoint(point: Point): void {
console.log(`x: ${point.x}, y: ${point.y}`);
}
const myPoint: Point = { x: 15, y: 25 };
displayPoint(myPoint);
- interface Point { x: number; y: number; }: Defines an interface named Point that describes an object with x and y properties, both of type number.
- Function displayPoint(point: Point): void: Accepts an object adhering to the Point interface and logs its x and y values.
Output:
x: 15, y: 25Type Aliases vs Interfaces in TypeScript
Type Aliases | Interfaces Type |
|---|---|
Type Aliases use the type keyword to define a new type. | Interface Type use the interface keyword to define a new type. |
Type aliases support extending other type aliases by intersection type. The & symbol is used to create an intersection type. Type aliases also extends interface types. | Interface Type also supports extending other interfaces by using the `extends` keyword. Interface type also extends type aliases. |
Type Aliases can be implemented by class with the use of the `implements` keyword. but they cannot be extended or implemented. | Interface Type can also be implemented by class with the use of the implements keyword. |
Type Aliases don't support declaration merging where declaring the same type of aliases again a second time with another type gives an error. | Interface type does support declaration merging where declaring the same interface again a second time merges with previous attributes of the last type interface. |
TypeScript Type Aliases vs. Interfaces - FAQs
Which one should I use for defining object shapes: Type Alias or Interface?
Interfaces are better for defining object shapes due to their support for extension and declaration merging. Type Aliases are useful for more complex or versatile types.
Can Type Aliases and Interfaces be implemented by classes in TypeScript?
Yes, both can be implemented by classes using the implements keyword. However, interfaces are preferred as they are specifically designed for defining object contracts.
Do Type Aliases and Interfaces have differences in compatibility with third-party libraries?
Interfaces often have better compatibility with TypeScript tooling and third-party libraries, making them more suitable for object-oriented programming scenarios.
Which is better for extending existing types: Type Alias or Interface?
Interfaces are more suitable for extending existing types due to their natural support for inheritance and declaration merging. Type Aliases can use intersections but lack declaration merging.
How do Type Aliases and Interfaces handle complex types like unions and intersections?
Type Aliases are better for defining unions (type A = B | C) and intersections (type A = B & C), while interfaces are limited in handling such complex types directly.
