What's the output?

Question

```javascript
class Counter {
  constructor() {
    this.count = 0;
  }

increment() {
    this.count++;
  }
}

const counterOne = new Counter();
counterOne.increment();
counterOne.increment();

const counterTwo = counterOne;
counterTwo.increment();

console.log(counterOne.count);
```

Accepted Answer

`counterOne` is an instance of the `Counter` class. The counter class contains a `count` property on its constructor, and an `increment` method. First, we invoked the `increment` method twice by calling `counterOne.increment()`. Currently, `counterOne.count` is `2`.

Then, we create a new variable `counterTwo`, and set it equal to `counterOne`. Since objects interact by reference, we're just creating a new reference to the same spot in memory that `counterOne` points to. Since it has the same spot in memory, any changes made to the object that `counterTwo` has a reference to, also apply to `counterOne`. Currently, `counterTwo.count` is `2`. We invoke `counterTwo.increment()`, which sets `count` to `3`. Then, we log the count on `counterOne`, which logs `3`.

関連概念

どのコンストラクタを使えば `Dog` classを継承できるでしょうか？

What's the output?

What's the output?

関連概念

関連概念

どのコンストラクタを使えば `Dog` classを継承できるでしょうか？

What's the output?

What's the output?

関連概念