fix(wepack.config.prod.js): set ecma option for compress and output to 5

[meandmax]

The current configuration of UglifyJS breaks in IE11 under specific circumstances.

39d6c62

I simply copied the configuration of the create-react-app master (not yet merged) and tested it works just fine.

https://medium.com/@_meandmax_/react-16-cra-and-ie11-giving-me-headaches-c8be43b4fcb2

Here is the link to the discussion in CRA where you can also find the configuration:
facebook/create-react-app#4234

Was not so sure if this is the right way to do this, but 2.14 breaks in IE11.

[DorianGrey]

Just to note - there was already a bug report on this: #288

Background: uglifyjs applies optimizations affecting size with respecting the ecma version in its compress resp. output options. That also includes rewriting an object definition to a shorthand version in case this is natively supported in the provided ecma version. However, this contradicts the target version provided to the typescript compiler, and that's why you end up with minified ES6+ code even though the compiler was told to provide ES5-compatible output.

Theoretically, the best option would be to pick up the target version from the tsconfig and map it to the version number required here; however, that's something even more complicated...

I.e.: LGTM, thanks!

[thomastvedt]

So.. I love IE 11 and just upgraded "react-scripts-ts": "2.15.1", but when running yarn start I get this in IE11:

But this should use react-scripts-ts/config/webpack.config.dev.js right? And not the webpack.config.prod.js? I don't see any Uglify plugin in dev-mode?

The production build seems to work (start at least) in IE11, but how can I get a development environment up and running while testing in IE11?

tsconfig.json:

   {
     "compilerOptions": {
       "outDir": "build/dist",
    "module": "esnext",
    "target": "es5",
    "downlevelIteration": false, 
    "importHelpers": false,
    "lib": ["es6", "es2016", "dom", "dom.iterable", "es2015.iterable"],
    "sourceMap": true,
    "jsx": "react",
    "moduleResolution": "node",
    "rootDir": "src",
    "forceConsistentCasingInFileNames": true,
    "baseUrl": "src",
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "suppressImplicitAnyIndexErrors": true,
    "noUnusedLocals": false,
    "allowSyntheticDefaultImports": true,
    "removeComments": true,
    "strict": false
  },
  "exclude": [
    "node_modules",
    "build",
    "dist",
    "scripts",
    "acceptance-tests",
    "webpack",
    "jest",
    "src/setupTests.ts"
  ]
}