TypeScript Object Interfaces vs. Intersections

TypeScript offers several features when it comes to defining complex data structures. In TypeScript, Object Interface and Intersections are two different features that serve different purposes when it comes to defining complex data structures.

Object Interfaces

• Object Interfaces are used to define the shape or structure of an object.
• They define the properties with the types that an object should contain.
• We use the ‘interface‘ keyword to declare an object interface followed by the interface name and its properties.
• They can be implemented by other interfaces and classes, promoting code reusability and maintainability.

Example: This example shows the use of the TypeScript Interfaces.

Javascript

interface Employee {
    eid: string,
    name: string
}
const emp: Employee = {
    eid: "E54321",
    name: "Ravi"
};

console.log(emp);

Output:

{ eid: 'E54321', name: 'Ravi' }

Intersections

• Intersections allow us to combine multiple types into a single type.
• We use the ‘&‘ operator to merge all properties and methods of each type involved.
• Intersections are used to compose multiple types by merging existing types or interfaces.

Example: This example shows the use of TypeScript intersections

Javascript

interface Employee {
    eid: string,
    name: string
}
interface Address {
    street: string;
    city: string;
}

type EmployeeWithAddress =
    Employee & Address;

const employeeWithAddress:
    EmployeeWithAddress = {
    eid: "E54321",
    name: "Bob",
    street: "123 BHU Lanka",
    city: "Varanasi",
};

console.log(employeeWithAddress);

Output:

{
  eid: 'E54321',
  name: 'Bob',
  street: '123 BHU Lanka',
  city: 'Varanasi'
}

Object Interfaces vs. Intersections:

Feature	Interface	Intersection
Purpose	Define shape of an object.	Combines multiple types into single type.
Declaration Syntax	Uses ‘interface’ keyword.	Uses ‘&’ Operator.
Structure	Defines properties with their types.	Merges properties and methods from multiple types.
Extensibility	Can be extended and implemented by other interfaces or classes.	Cannot be extended.
Composition	Support extending interface with help of inheritance.	Combines multiple type or interfaces without inheritance.
Object Instances	Used to declare objects that conform to the interface.	Not used directly to declare objects.
Reusability	Objects are reusable due to inheritance.	Used to create advance composite types.
Use Cases	Defining individual object structures.	Used when we want to create a new type that has characteristics of multiple types.

Conclusion: TypeScript object interfaces are used to define the structure of individual objects, while intersections combine multiple types to create new composite types. In many cases, we might use both object interfaces and intersections depending on the specific requirements of our applications. Understanding when and how to use these powerful features is essential for building robust applications using TypeScript.