"Module parse failed: Unexpected token" when added the class field - node.js

Question

Below TypeScript code (it means that static class fields and other TypeScript features are available) successfully has been built with Webpack:
export default class ConfigRepresentative {
constructor() {
console.log('ok');
}
}
Fails (same if to remove private and static):
export default class ConfigRepresentative {
private static ownInstanceHasBeenCreated: boolean = false;
constructor() {
console.log('ok');
}
}
Error:
ERROR in ./TypeScriptSource/index.ts 7:10
Module parse failed: Unexpected token (7:10)
You may need an appropriate loader to handle this file type.
| export default class ConfigRepresentative {
|
> private static ownInstanceHasBeenCreated: boolean = false;
|
| constructor() {
webpack.config.js
module.exports = {
entry: './TypeScriptSource/index.ts',
output: {
filename: 'index.js',
path: __dirname,
libraryTarget: 'umd'
},
target: 'node',
mode: 'production',
watch: true,
module: {
rules: [
{
test: /\.ts?$/,
use: 'ts-loader',
exclude: /node_modules/
}
]
},
resolve: {
extensions: ['.ts', '.js']
}
};
For saving your time on reproducing this problem, I attached the souse files.
error.zip

Answer 1

It is because the project was inside node_modules folder. The setting exclude: /node_modules/ cancels the rule {test: /\.ts?$/, use: 'ts-loader'}, but without class property code is pure JavaScript.
(I know that it is bad practice - to develop something inside node_modules, however I don't know the other solution for developing dependencies. In this case, single ConfigRepresentative is useless if it does not used by other project).