Webpack + React + TypeScript: Module not found ... in ... node_modules/react/

Webpack is not resolving .js files. Add this to your webpack.config.js.

resolve: {
    extensions: [".ts", ".tsx", ".js", ".jsx"]
},

Here is the tsconfig.json I used to run your example.

{
  "compilerOptions": {
    "jsx": "react",
    "lib": ["es6", "dom"],
    "rootDir": "src",
    "module": "commonjs",
    "target": "es5",
    "sourceMap": true,
    "moduleResolution": "node",
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "noImplicitAny": true,
    "strictNullChecks": true
  },
  "include": [
    "./src"
  ],
  "exclude": [
    "node_modules",
    "build"
  ]
}