Angular: ERROR in No NgModule metadata found for 'AppModule'

When trying to run an angular app I was getting the error:

ERROR in No NgModule metadata found for 'AppModule'.

The error could possibly be becuase of following reasons:

1. There is a statement of the form 
   platformBrowserDynamic().bootstrapModule(App)
   in main.ts file where App is not really a module. Solution is to reaplace App with AppModule
2. The patformBrowserDynamic variable is declared as a constant 

   const platform = platformBrowserDynamic();
   platform.bootstrapModule(App);

   Solution is remove const keyword
3. And sometimes if the compiler fails for any unknown reason, try editing app.module.ts file (like deleting and reinserting a character). After saving the file the app is automatically recompiled and starts working normally if it has already been started using ng serve or npm start.

Stackoverflow reference:

https://stackoverflow.com/questions/39685179/angular-2-no-ngmodule-metadata-found