How to resolve: Cannot determine the module for class OverlayPortal

Issue

I'm facing following issue: If I try to build my Ionic 3 app for ios with the --prod flag, I get following error:

typescript error
Cannot determine the module for class OverlayPortal in
C:/.../node_modules/ionic-angular/umd/components/app/overlay-portal.d.ts!
Add OverlayPortal to the NgModule to fix it. Cannot determine the module for class IonicApp in
C:/.../node_modules/ionic-angular/umd/components/app/app-root.d.ts! 
Add IonicApp to the NgModule to fix it. Cannot determine the module for class ClickBlock in
C:/.../node_modules/ionic-angular/umd/components/app/click-block.d.ts! 
Add ClickBlock to the NgModule to fix it.

Build command used:

ionic cordova build ios --prod

The error does not appear if I build without the --prod flag or if I use ionic serve. I'm not using any of the classes mentioned in the error message in my code.

Solution

I resolved the issue by searching through my code and removing any reference to Ionics Page class, which is suggested here.

Example: Turn let page : Page; into let page;

Also make sure to remove any imports of the Page class, which might look like this:

import { Page } from 'ionic-angular/umd/navigation/nav-util';

Answered By - Phonolog