event handler binding

Question

I see that one approach to binding event handlers in React is doing it in the constructor. As per the docs:
```javascript
class Foo extends Component {
constructor() {
    super();
    this.handleClick = this.handleClick.bind(this);
  }
  handleClick() {
    console.log('Click happened');
  }
}
```
My question is how can we call the bind function on this.handleClick before the method is even defined? I believe the constructor is the first code to run when a new instance of Foo is created, so why isn't this.handleClick undefined
javascript
this.handleClick = this.handleClick.bind(this);

if handleClick() is defined below that? Some kind of hoisting?

Brendan Whiting · Accepted Answer

I'm going to tentatively answer this, because I'm not 100% sure. But I think the reason it works is that handleClick gets defined on the prototype, so then it's there when you create an instance later. It's not hoisting.
Side note, arrow functions make this so much better. You can assign an arrow function to a class property instead of using a class method, and then you don't have call .bind() on it in order to pass it down as an event handler. (This is covered in other videos/courses)

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Axel Perossa

Axel Perossa

event handler binding

1 Answer

Brendan Whiting

Brendan Whiting