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Update plugin-proposal-decorators.md #1914

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Update plugin-proposal-decorators.md
mountainmoon Dec 11, 2018
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Update plugin-proposal-decorators.md
mountainmoon Dec 12, 2018
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54 changes: 42 additions & 12 deletions docs/plugin-proposal-decorators.md
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Expand Up @@ -6,16 +6,26 @@ sidebar_label: proposal-decorators

## Example

(examples are from proposal)

### Simple class decorator

```js
@annotation
class MyClass { }

function annotation(target) {
target.annotated = true;
function annotation(classDescriptor) {
return {
...classDescriptor,
elements: [
...classDescriptor.elements,
{
kind: 'field',
key: 'annotated',
placement: 'static',
descriptor: {},
initializer: () => true
}
]
};
}
```

Expand All @@ -26,9 +36,21 @@ function annotation(target) {
class MyClass { }

function isTestable(value) {
return function decorator(target) {
target.isTestable = value;
}
return function(classDescriptor) {
return {
...classDescriptor,
elements: [
...classDescriptor.elements,
{
kind: 'field',
key: 'isTestable',
placement: 'static',
descriptor: {},
initializer: () => value
}
]
};
};
}
```

Expand All @@ -41,13 +63,20 @@ class C {
}

function enumerable(value) {
return function (target, key, descriptor) {
descriptor.enumerable = value;
return descriptor;
}
return function(elementDescriptor) {
return {
...elementDescriptor,
descriptor: {
...elementDescriptor.descriptor,
enumerable: value
}

@nicolo-ribaudo nicolo-ribaudo Dec 12, 2018

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All this function can be simplified to

return function(elementDescriptor) {
  elementDescriptor.descriptor.enumerable = value;
};

@mountainmoon mountainmoon Dec 13, 2018 •
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I just noticed the examples of the latest proposal were wrote in immutable style. But it looks like not necessary.
So the others can also be simplified to

function annotation(classDescriptor) {
  classDescriptor.elements.push({
    kind: 'field',
    key: 'annotated',
    placement: 'static',
    descriptor: {},
    initializer: () => true,
  });
}

function isTestable(value) {
  return function(classDescriptor) {
    classDescriptor.elements.push({
      kind: 'field',
      key: 'isTestable',
      placement: 'static',
      descriptor: {},
      initializer: () => value,
    });
  };
}

It works in Babel 7.1.0. However, the proposal said a decorator function returns a decorator. So should I add a return ?

return function(elementDescriptor) {
  elementDescriptor.descriptor.enumerable = value;
  return elementDescriptor
};

@nicolo-ribaudo nicolo-ribaudo Dec 13, 2018

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If a decorator returns nothing, it returns the original descriptor (probably that introduction needs to be updated, in you want to open a PR).

I'd like to have examples in both styles, to show different ways of using decorators.

};
};
}
```

[For further examples.][proposal]

## Installation

```sh
Expand Down Expand Up @@ -142,5 +171,6 @@ Right:

## References

* [Proposal: JavaScript Decorators](https://github.com/wycats/javascript-decorators/blob/master/README.md)
* [Proposal: JavaScript Decorators][proposal]

[proposal]: https://github.com/tc39/proposal-decorators/blob/master/README.md