How/Why TypeScript awesome?

情境 1. 當要修改 code 的時候

參數 payload 該丟什麼？

情境 2. 天殺的就是有人手賤，時

那如果用了 TypeScript...?

同場加映

問題之一: destructing 會造成 confusing

function createOrUpdateProject({ payload: { key: string, value: string } }) {
  return {
    type: 'CREATE_OR_UPDATE_PROJECT',
    payload: {
      key,
      value,
    }
  }
}

function createOrUpdateProject({ payload as { key: string, value: string } }) {
  return {
    type: 'CREATE_OR_UPDATE_PROJECT',
    payload: {
      key,
      value,
    }
  }
}

問題之二: Type Hint 其實不好超難讀

問題之三: Type Detection 不夠聰明

Programming language design does have a concept of bottom type that is a natural outcome as soon as you do code flow analysis. TypeScript does code flow analysis (😎) and so it needs to reliably represent stuff that might never happen.

The never type is used in TypeScript to denote this bottom type. Cases when it occurs naturally:

A function never returns (e.g. if the function body has while(true){})
A function always throws (e.g. in function foo(){throw new Error('Not Implemented')} the return type of foo is never)

問題之三: Default Type 黑人問號

為什麼不是 void? 讓我們看下去...

The Any type is used to represent any JavaScript value. The Any type is a supertype of all types and is assignable to and from all types. In general, in places where a type is not explicitly provided and TypeScript cannot infer one, the Any type is assumed.

So.....

Any ≠ Void (Swift)

Any ≠ Void (Kotlin)

any = void (TypeScript)

問題之四: 認真 OOP

以 overload 為例

問題之四: 認真 OOP 之 Overload

class User {
  func register(name: String, gender: Gender, age: Int) {
    ...
  }
  func register(facebookID: String, gender: Gender) {
    ...
  }
  func register(referURL: URL) {
    ...
  }
}

protocol User {
  func register(name: String, gender: Gender, age: Int)
  func register(facebookID: String, gender: Gender)
  func register(referURL: URL)
}

我所知道的 Overload - Swift version

推論之後試著套用在 TypeScript 上

class User {
  register(name: string, gender: Gender, age: number): void {
    ...
  }
  register(facebookID: string, gender: Gender): void {
    ...
  }
  register(referURL: URL): void {
    ...
  }
}

🚫

class User {
  register(name: string, gender: Gender, age: number): void;
  register(facebookID: string, gender: Gender): void;
  register(referURL: URL): void;
  register(nameOrFacebookIDOrReferURL: URL | string, gender?: Gender, age?: number): void {
    ......
  }
}

✅

問題之四: 認真 OOP 之 Overload

同場加映啦！🎉

那 interface 如何？

interface User {
  register(name: string, gender: Gender, age: number): void;
  register(facebookID: string, gender: Gender): void;
  register(referURL: URL): void;
  register(nameOrFacebookIDOrReferURL: URL | string, gender?: Gender, age?: number): void;
}

interface User {
  register(name: string, gender: Gender, age: number);
  register(facebookID: string, gender: Gender);
  register(referURL: URL);
}
const user: User {
  ...
  register(nameOrFacebookIDOrReferURL: URL | string, gender?: Gender, age?: number) {
    ......
  }
}
// Or
class Member implements User {
  ...
  register(nameOrFacebookIDOrReferURL: URL | string, gender?: Gender, age?: number) {
    ......
  }
}

問題之四: 認真 OOP 之 UnionType

問題之四: 認真 OOP 之 blablabla

問題之五: 文件保證胃痛呢微軟同一系品質

WRAP IT UP

THE END

Thanks for listening