Angular issue while extending a subject class in Angular 10 in production mode

🐞 bug report

Affected Package

The issue is caused by package "@angular/animations": "~10.0.5",

"@angular/common": "~10.0.5",
"@angular/compiler": "~10.0.5",
"@angular/core": "~10.0.5",
"@angular/forms": "~10.0.5",
"@angular/platform-browser": "~10.0.5",
"@angular/platform-browser-dynamic": "~10.0.5",
"@angular/router": "~10.0.5",

Is this a regression?

Yes, the previous version(Angular 9) in which this bug was not present and this issue did not exist in Angular 11 also.

This issue only exists in Angular 10 only

Description

we have a subject class in our project: “export class OrdersService extends Subject <DataSource_1>”

while extending that subject class in Angular 10 in Production mode.

We have been getting null value while extending and the following error:

“Uncaught TypeError: Class extends value undefined is not a constructor or null”.

🔬 Minimal Reproduction

This issue occurred due to extends the “Subject” class in Angular 10 in production mode.

“export class OrdersService extends Subject <DataSource_1>”

🔥 Exception or Error

**"Uncaught TypeError: Class extends value undefined is not a constructor or null".**

🌍 Your Environment

Angular Version:

"@angular/animations": "~10.0.5",
    "@angular/common": "~10.0.5",
    "@angular/compiler": "~10.0.5",
    "@angular/core": "~10.0.5",
    "@angular/forms": "~10.0.5",
    "@angular/platform-browser": "~10.0.5",
    "@angular/platform-browser-dynamic": "~10.0.5",
    "@angular/router": "~10.0.5",

Anything else relevant?

[mlc-mlapis]

@praveenkumargspr As in many other cases, here, without a simple reproduction demo, it’s unrealistic that anybody can help with it. And the simple means really simple = with minimal dependencies, with code reduced only to the minimum of lines to make it as readable as possible.

[petebacondarwin]

Please can you provide a reproduction of this problem that we can view?