> Le 28 déc. 2014 à 22:42, Антон Шувалов <[email protected]> a écrit :
>
> Hi, guys! I'm confused with class properties. With prototype chains I can
> setup kinda default values which being replaced by values from children. But
> replacing become hard to work with classes. For example, we have simple
> module, some backbone view:
>
> ```js
> class BaseView extends Backbone.View {
> constructor() {
> this.tagName = 'div';
> super(); // create element from this.tagName value
> }
> }
> ```
>
> And now we create inherited view:
>
> ```js
> class Span extends BaseView {
> constructor() {
> this.tagName = 'span'
> super();
> }
> }
> ```
>
> But all `this` variables will be replaced by parent, not by child. It's kinda
> weird. Another example with prototype chains works fine:
>
> ```js
> var BaseView = Backbone.View.extends({
> tagName: 'div'
> })
> ```
>
> ```js
> var Span = Backbone.View.extends({
> tagName: 'span'
> });
> ```
>
> How I can do similar things with es6 classes? Sorry if this question is
> already discussed.
There is more than one way to resolve your problem. Here are those I see:
(1) Use a getter:
```js
class BaseView extends Backbone.View {
get tagName() {
return 'div'
}
}
```
(2) If the super constructor supports it, adjust the property after having
called the super constructor:
```js
class BaseView extends Backbone.View {
constructor() {
super()
this.tagName = 'div'
}
}
```
(3) Otherwise, test if your property is already defined:
```js
class BaseView extends Backbone.View {
constructor() {
if (this.tagName === undefined)
this.tagName = 'div'
super()
}
}
```
But it is not considered good style to send implicit parameters to the
super-constructor through properties of the instance being constructed. You
smell it when you see references to `this` before the call to `super()`. At
this point, it may be preferable to refactor the code and make all parameters
explicit:
```js
class BaseView extends Backbone.View {
constructor(params = {}) {
if (params.tagName === undefined)
params.tagName = 'div'
super(params)
}
}
```
—Claude
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