introduce check type definition

demo-shell-ng2/config/webpack.common.js

@@ -4,6 +4,7 @@ const CopyWebpackPlugin = require('copy-webpack-plugin');
 const ExtractTextPlugin = require("extract-text-webpack-plugin");
 const helpers = require('./helpers');
 const path = require('path');
+const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');
 
 module.exports = {
     entry: {
@@ -84,6 +85,7 @@ module.exports = {
     },
 
     plugins: [
+        new ForkTsCheckerWebpackPlugin(),
         // Workaround for angular/angular#11580
         new webpack.ContextReplacementPlugin(
             // The (\\|\/) piece accounts for path separators in *nix and Windows