What distinguishes interfaces from classes in TypeScript, and in which situations is each used?

In TypeScript, interfaces and classes have different purposes and features:

• Interfaces describe the structure of data — what properties and methods an object should have. They do not contain implementation, serving for typing and contracts.
• Classes are templates for creating objects with method implementations and state (properties). Classes can contain constructors, methods with bodies, and access modifiers.

When to use:

• Interfaces are used to describe data formats, especially when only the structure matters, such as for function parameters or objects.
• Classes are used when logic implementation, creating instances with behavior, and inheritance are needed.

Example of an interface:

interface IUser {
  id: number;
  name: string;
}

Example of a class:

class User implements IUser {
  constructor(public id: number, public name: string) {}
  greet() {
    console.log(`Hello, ${this.name}`);
  }
}

Thus, interfaces are contracts, and classes are concrete implementations with behavior.