This is temporary version of @ngtools/webpack package that doesn't strip off custom decorators from code. It will be deprecated when https://github.com/angular/angular-cli/issues/2799 is resolved.

Get it from npm:

npm install --save ngtools-webpack-keep-decorators

Change ngtools import:

const ngtools = require('@ngtools/webpack') => const ngtools = require('ngtools-webpack-keep-decorators')

And update your loader:

loaders: ['@ngtools/webpack'] => loaders: ['ngtools-webpack-keep-decorators']