Steps to reproduce

• tns create Sample --ng
• Now add for example yellow background to the sample StackLayout
  app.component.ts:

...
@Component({
 selector: "my-app",
 templateUrl: "app.component.html",
 styleUrls: [ "app.component.css" ]
})
...

app.component.css:

StackLayout {
 background-color: yellow;
}

• tns install webpack
• tns prepare ios --emulator --bundle
• tns run ios --emulator --bundle

Till there all looks correct:
simulator screen shot nov 12 2016 06 49 46

Now add the uglification:

• npm install webpack --save-dev
• tns prepare ios --emulator --bundle
• tns run ios --emulator --bundle
• Adjust the webpack config:
  webpack.config.js:

var bundler = require("nativescript-dev-webpack");
var webpack = require("webpack");
module.exports = bundler.getConfig({
 plugins: [
 new webpack.optimize.UglifyJsPlugin({
 comments: false,
 compress: { warnings: false }
 })
 ]
});

And there is where the error occurs:
simulator screen shot nov 12 2016 06 55 22