minor fixes

This commit is contained in:
Ilya Kantor 2020-04-04 15:15:09 +03:00
parent 2acd2584d7
commit 23ffde7806

View file

@ -333,8 +333,6 @@ Technically, they are processed after the constructor has done it's job.
### Making bound methods with class fields
Class fields together with arrow functions can be used to create "bound" methods, with fixed `this` that always references the object.
As demonstrated in the chapter <info:bind> functions in JavaScript have a dynamic `this`. It depends on the context of the call.
So if an object method is passed around and called in another context, `this` won't be a reference to its object any more.
@ -361,17 +359,17 @@ setTimeout(button.click, 1000); // undefined
The problem is called "losing `this`".
There are two ways to fix it, as discussed in the chapter <info:bind>:
There are two approaches to fixing it, as discussed in the chapter <info:bind>:
1. Pass a wrapper-function, such as `setTimeout(() => button.click(), 1000)`.
2. Bind the method to object in the constructor:
2. Bind the method to object, e.g. in the constructor:
```js run
class Button {
constructor(value) {
this.value = value;
*!*
this.click = this.click.bound(this);
this.click = this.click.bind(this);
*/!*
}
@ -406,7 +404,7 @@ let button = new Button("hello");
setTimeout(button.click, 1000); // hello
```
As you can see, `click = () => {...}` creates an independent function on each `Button` object, with `this` bound to the object.
The class field `click = () => {...}` creates an independent function on each `Button` object, with `this` bound to the object. Then we can pass `button.click` around anywhere, and it will be called with the right `this`.
That's especially useful in browser environment, when we need to setup a method as an event listener.