Typescript
Private Protected

public, private, protected

Public

class Animal {
  public name: string;
 
  public constructor(input: string) {
    this.name = input;
  }
 
  eat(something: string) {
    console.log(`I just ate ${something}`);
  }
}

default 宣告都是屬於 public，沒有什麼限制。

Private

Javascript ES10 支援用#來表示 private members，Typescript 在 3.8 版本中跟上，另外也提供用 private 這個字來宣告成員，無法在 Class 外存取。

（但 typescript 只是在 compile 階段提醒）

Typescript (opens in a new tab)

class Animal {
  private name: string;
  constructor(name: string) {
    this.name = name;
  }
}
 
const animal1 = new Animal("animal1");
 
console.log(animal1.name);
// [LOG]: Property 'name' is private and only accessible within class 'Animal'.
// 只能在原class內存取private member
 
class Animal {
  private name: string;
  constructor(name: string) {
    this.name = name;
  }
}
 
class Cat extends Animal {
  private color: string;
  constructor(name: string, color: string) {
    super(name);
    this.color = color;
  }
 
  moew() {
    console.log(this.name);
    // [LOG]: Property 'name' is private and only accessible within class 'Animal'.
    // 加一個貓貓subclass，因為name是private即使subclass在class內一樣不能存取。
  }
}

Protected

如果想要讓 subclass 可以在 class 內用，可以用 protected。

class Animal {
  protected name: string;
  constructor(name: string) {
    this.name = name;
  }
}
 
const animal1 = new Animal("animal1");
 
console.log(animal1.name);
// [LOG]: Property 'name' is protected and only accessible within class 'Animal' and its subclasses.
// 跟private一樣不能從class外取用
 
class Cat extends Animal {
  private color: string;
  constructor(name: string, color: string) {
    super(name);
    this.color = color;
  }
 
  meow() {
    console.log(this.name);
    // subclass可以在class內取用
  }
}
 
const latte = new Cat("Latte", "Orange");
 
latte.meow();
// [LOG]: "Latte"
// 在subclass中也可以透過class內method存取
 
console.log(latte.name);
// [LOG]: Property 'name' is protected and only accessible within class 'Animal' and its subclasses.
// 但跟private一樣不能從外取用