7 ترفند مخفی TypeScript که حرفه ای ها از آنها استفاده می کنند 😎🤫

enum CounterActionType {
  Increment = "INCREMENT",
  IncrementBy = "INCREMENT_BY",
}

interface IncrementAction {
  type: CounterActionType.Increment;
}

interface IncrementByAction {
  type: CounterActionType.IncrementBy;
  payload: number;
}

type CounterAction =
  | IncrementAction
  | IncrementByAction;

function reducer(state: number, action: CounterAction) {
  switch (action.type) {
    case CounterActionType.Increment:
      // TS infers that the action is IncrementAction
      // & has no payload
      return state + 1;
    case CounterActionType.IncrementBy:
      // TS infers that the action is IncrementByAction
      // & has a number as a payload
      return state + action.payload;
    default:
      return state;
  }
}

type Status = "idle" | "loading" | "success" | "error";

type Review = 1 | 2 | 3 | 4 | 5;

// or better yet:
const reviewMap = {
  terrible: 1,
  average: 2,
  good: 3,
  great: 4,
  incredible: 5,
} as const;

// This will generate the same type as above,
// but it's much more maintainable
type Review = typeof reviewMap[keyof typeof reviewMap];

function isNumber(value: any): value is number {
  return typeof value === "number";
}

const validateAge = (age: any) => {
  if (isNumber(age)) {
    // validation logic
    // ...
  } else {
    console.error("The age must be a number");
  }
};

const validateAge = (age: number) => {
  // ...
};

enum PaticipationStatus {
  Joined = "JOINED",
  Left = "LEFT",
  Pending = "PENDING",
}

interface ParticipantData {
  [id: string]: PaticipationStatus;
}

const participants: ParticipantData = {
  id1: PaticipationStatus.Joined,
  id2: PaticipationStatus.Left,
  id3: PaticipationStatus.Pending,
  // ...
};

const clone = <T>(object: T) => {
  const clonedObject: T = JSON.parse(JSON.stringify(object));
  return clonedObject;
};

const obj = {
  a: 1,
  b: {
    c: 3,
  },
};

const obj2 = clone(obj);

const ErrorMessages = {
  InvalidEmail: "Invalid email",
  InvalidPassword: "Invalid password",
  // ...
} as const;

// This will throw an error
ErrorMessages.InvalidEmail = "New error message";

interface User {
  name: string;
  age?: number;
  email: string;
}

type PartialUser = Partial<User>;
type PickUser = Pick<User, "name" | "age">;
type OmitUser = Omit<User, "age">;
type RequiredUser = Required<User>;

// PartialUser is equivalent to:
// interface PartialUser {
//   name?: string;
//   age?: number;
//   email?: string;
// }

// PickUser is equivalent to:
// interface PickUser {
//   name: string;
//   age?: number;
// }

// OmitUser is equivalent to:
// interface OmitUser {
//   name: string;
//   email: string;
// }

// RequiredUser is equivalent to:
// interface RequiredUser {
//   name: string;
//   age: number;
//   email: string;
// }

type A = B & C;