Fixed 'is undefined' error and prop checking in Async example

[leiming]

Fix the same error as #2464 #2459 for Async example.

If it is acceptable, I will fix all examples which includes #2469

[timdorr]

Does our/CRA's eslint config not support class properties and statics?

[leiming]

Thanks for replying, @timdorr.

I think CRA's ESLint has supported babel-plugin-transform-class-properties. However it doesn't take effort in example cases.

I try to add a .eslintrc file in redux/examples/real-world/src, and even install both babel-plugin-transform-class-properties and babel-preset-react-app:

{
  "extends": "react-app",
  "plugins": ["transform-class-properties"]
}

then:

cd redux/examples/real-world/src
yarn add -D babel-preset-react-app babel-plugin-transform-class-properties
yarn start

It still throws error, seems ignore all ESLint config:

Failed to compile.

./src/containers/App.js
  Line 9:   'propTypes' is not defined           no-undef
  Line 18:  'handleDismissClick' is not defined  no-undef
  Line 23:  'handleChange' is not defined        no-undef

Search for the keywords to learn more about each error.

[timdorr]

Oh, this looks like it's coming from the eslint install at the root of the repo: facebook/create-react-app#2604 (comment)

Downgrading back to eslint 3.x should fix it, I believe.

[leiming]

OK, I will keep track of facebook/create-react-app#2644

[timdorr]

Since it's something that will be fixed upstream, I'll wait on that fix before making code changes here. Thanks for bringing this to our attention!