Typescript patterns

in-operator.ts

// Use the Javascript "in" operator for automatic type inference
// https://egghead.io/lessons/typescript-use-the-javascript-in-operator-for-automatic-type-inference-in-typescript

interface Admin {
  id: string;
  role: string;
}

interface User {
  email: string;
}

function redirect(user: Admin | User) {
  if ("role" in user) {
    // The type is Admin, because it has a property "role"
    console.log(user.role);
  } else {
    console.log(user.email);
  }
}

ts-swtich-case.ts

// https://github.com/eggheadio-projects/practical-advanced-typescript-features/tree/4-infer-type-switch-statement

interface Action {
  type: string;
}

const AddPerson = {
  type = "Add",
};