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Type queries and indexed access types

1. Type Queries​

keyof Operator​

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

type DatePropertyNames = keyof Date; // This will return all the properties of Date type.

typeof Operator​

The typeof operator is used to get the type of a variable or property. It will always return a string.

async function main() {
  const response = await Promise.all([
    fetch("https://jsonplaceholder.typicode.com/todos/1"),
    Promise.resolve(10),
  ]);

  type Response = typeof response; // This will return the type of response variable.
}

2. Indexed Access Types​

Indexed access types are used to get the type of a property within an object.

const person = {
  name: "John",
  age: 30,
  color: {
    primary: "red",
    secondary: "blue",
  },
};

type ColorType = (typeof person)["color"]; // This will return the type of color property of person object.

3. Type Registry Pattern​

The Type Registry Pattern allows you to define reusable and type-safe objects, but we'll need more details to explain this pattern further. The concept can be extended to various use cases.