Single and multiple inheritance

⬅️ FEM TypeScript Fundamentals

Single and multiple inheritance

• In JavaScript and TypeScript, classes can only extend one other class. This is called “single inheritance”, in contrast to the “multiple inheritance” allowed by some other languages.
• Implementing two incompatible interfaces doesn’t give us a never type. Instead, it causes an error directly in the class definition.

interface NameMustBeString {
  name: string
}
 
interface NameMustBeNumber {
  name: number
}
 
class User implements NameMustBeString, NameMustBeNumber {
  name: string;
  
  constructor(name: string) {
    this.name = name;
  }
}
 
const amir = new User('Amir');
amir.name;
 
//Result:
type error: Property 'name' in type 'User' is not assignable to the same property in base type 'NameMustBeNumber'.
  Type 'string' is not assignable to type 'number'.