FAQ: TypeScript

What does typeof operator do?

The typeof operator returns the data type of a variable or an expression. It is a unary operator that is placed before its operand.

const book = {
  title: 'JavaScript',
  author: 'John Doe',
};
console.log(typeof book); // object

What does keyof operator do?

The keyof operator returns the keys of a type. It is used to get the keys of an object type.

type Book = {
  title: string;
  author: string;
};

type BookKeys = keyof Book; // 'title' | 'author'