What are some examples of declaration merging in TypeScript?

What are some examples of declaration merging in TypeScript?

Declaration merging in TypeScript allows you to define multiple declarations for the same entity. For example, if you have an interface and you declare it again with additional properties, TypeScript will merge them into a single interface.

Can you give me a specific code example?

Sure! Here's a simple example:

interface User {
  name: string;
}

interface User {
  age: number;
}

const user: User = {
  name: 'Alice',
  age: 30
};

In this case, the User interface has been merged to include both name and age.

What happens if I declare a function with the same name multiple times?

If you declare a function with the same name multiple times, TypeScript will merge the signatures of those functions. However, the implementation must be provided only once.

Are there any limitations to declaration merging?

Yes, there are some limitations. For instance, merging only works with certain types like interfaces and namespaces, but not with classes or enums.