如何在JavaScript类之外访问类属性

Question

How is the sound property not properly private in this JavaScript class? Additionally, how can it be accessed outside the class? I saw this in a video and attempted to access the sound property outside the class and could not.

class Dog {
  constructor() {
    this.sound = 'woof';
  }
  talk() {
    console.log(this.sound);
  }
}

Thanks!!

Answer 1

It's not private because you can access it from the outside after creating an instance of the class.

 class Dog { constructor() { this.sound = 'woof'; } talk() { console.log(this.sound); } } let dog = new Dog(); console.log(dog.sound); // <-- // To further drive the point home, check out // what happens when we change it dog.sound = 'Meow?'; dog.talk(); 

Answer 2

You need to create an instance of the class using new . When you don't have an instance of the class, the constructor has yet to be executed, so there's no sound property yet.

var foo = new Dog();
console.log(foo.sound);

or

This will assign a default property to the Dog class without having to create a new instance of it.

Dog.__proto__.sound = 'woof';
console.log(Dog.sound);

Answer 3

You need to create instance of your class.

 class Dog { constructor() { this.sound = 'woof'; } talk() { console.log(this.sound); } } console.log(new Dog().sound);