Babel 7 does not need ts-loader.

As of Babel 7 the ts-loader is unnecessary, because Babel 7 understands TypeScript. Complete details of a TypeScript + Babel7 + Webpack setup are here.

An overview of the set up without ts-loader.

Install Babel's TypeScript support. Only @babel/preset-typescript is mandatory; the other three add additional features that TypeScript supports.

npm install --save-dev @babel/preset-typescript 
npm install --save-dev @babel/preset-env 
npm install --save-dev @babel/plugin-proposal-class-properties 
npm install --save-dev @babel/plugin-proposal-object-rest-spread

Configure the additional .babelrc plugins and presets.

{
    "presets": [
        "@babel/preset-env",
        "@babel/preset-typescript"
    ],
    "plugins": [
        "@babel/proposal-class-properties",
        "@babel/proposal-object-rest-spread"
    ]
}

And update your webpack.config.js (other code is omitted for clarity).

module: {
  rules: [
  {
     test: /\.(js|jsx|tsx|ts)$/,
     exclude: /node_modules/,
     loader: 'babel-loader'
    }
  ]
},
resolve: {
  extensions: ['*', '.js', '.jsx', '.tsx', '.ts'],
},

ts-loader: convert typescript (es6) to javascript (es6)

babel-loader: converts javascript (es6) to javascript (es5) and Typescript doesn't do polyfills, which babel does. If you write client-side code in es6 and want it to run on modern browsers, you'd probably need babel's polyfills.

It is less justified with server-side code - just use the latest node version for es6 support. But babel still provides some goodies that tsc doesn't - like caching, or a huge range of plugins that can be very useful.

It's not necessary but a practice for using them all together.

This babel-loader issue solved my problem.

You've got to add this to your webpack.config.js in order to make it resolve ts and tsx files.

webpack.config.js

resolve: {
  extensions: ['.ts', '.tsx', '.js', '.json']
}

These "getting started" instructions can be found here:

https://github.com/Microsoft/TypeScript-Babel-Starter#create-a-webpackconfigjs