This Bug is a starting Bug that must be fixed at the nearest delay.
> ionic start app0 aws // aws is a default starting app in Ionic3
> cd app0
> ionic serve
[app-scripts] [16:44:12] typescript: node_modules/aws-amplify/lib/PubSub/Providers/MqttOverWSProvider.d.ts, line: 2
[app-scripts] Cannot find type definition file for 'zen-observable'.
[app-scripts] L1: import { Client } from 'paho-mqtt';
[app-scripts] L2: import * as Observable from 'zen-observable';
[app-scripts] L3: import { AbstractPubSubProvider } from './PubSubProvider';
[app-scripts] [16:44:12] typescript: node_modules/aws-amplify/lib/PubSub/Providers/PubSubProvider.d.ts, line: 1
[app-scripts] Cannot find type definition file for 'zen-observable'.
[app-scripts] L1: import * as Observable from 'zen-observable';
[app-scripts] L2: import { PubSubProvider, ProvidertOptions } from '../types';
[app-scripts] Cannot find type definition file for 'zen-observable'.
[app-scripts] [16:44:12] typescript: node_modules/aws-amplify/lib/PubSub/PubSub.d.ts, line: 1
[app-scripts] L1: import '../Common/Polyfills';
[app-scripts] L2: import * as Observable from 'zen-observable';
[app-scripts] [16:44:12] typescript: node_modules/aws-amplify/lib/PubSub/types/Provider.d.ts, line: 1
[app-scripts] Cannot find type definition file for 'zen-observable'.
[app-scripts] L1: import * as Observable from 'zen-observable';
[app-scripts] L2: import { ProvidertOptions } from './PubSub';
````Preformatted text`
>
> Ionic:
>
> ionic (Ionic CLI) : 4.3.1
>
> System:
>
> NodeJS : v8.9.4
> npm : 6.4.1
> OS : Linux 4.13