Repository: create-react-app
Issue: decorators on generator functions parse error with --typescript
Labels: issue: needs investigation,issue: typescript

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npm --version
6.4.1

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decorators on generator functions parse error with --typescript

### Environment

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Environment Info:

  System:
    OS: Windows 10
    CPU: x64 Intel(R) Xeon(R) CPU E5-2630 v3 @ 2.40GHz
  Binaries:
    Yarn: 1.10.1 - C:\Program Files\nodejs\yarn.CMD
    npm: 6.1.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: 42.17134.1.0
    Internet Explorer: 11.0.17134.1
  npmPackages:
    react: ^16.8.4 => 16.8.4
    react-dom: ^16.8.4 => 16.8.4
    react-scripts: Not Found
  npmGlobalPackages:
    create-react-app: Not Found
### Steps to Reproduce

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(Write your steps here:)

1.  create-react-app my-app typescript
2.  add experimentalDecorators in tsconfig.json
3.  add related code 
```
@effect() // define async action handle
    * addAsync(count: number) {
        yield delay(2000);
        this.add(count); // type check here
    }
```


### Expected Behavior

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parse success 
### Actual Behavior

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```
./src/AppModel.ts
SyntaxError: C:\Users\zeroone\Desktop\my-app\src\AppModel.ts: Unexpected token (17:30)

  15 | export default class AppModel extends Model<AppState> {
  16 |     @effect() // define async action handle
> 17 |     * addAsync(count: number) {
     |                               ^
  18 |         yield delay(2000);
  19 |         this.add(count); // type check here
  20 |     }
```

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