IE11: ng test with differential loading: syntax error when fast-check is used

🐛 Bug Report

If fast-check is added to a spec in a fresh Angular 9.1.12 project with differential loading turned on, Karma will report a syntax error in IE11. Upon investigation it seems, that a “class” keyword lands in the vendor.js bundle served by angular:

class ArrayArbitrary extends _definition_Arbitrary_js__WEBPACK_IMPORTED_MODULE_2__["Arbitrary"] {
//... it looks like further definitions from fast-check follow this line.

To Reproduce

See example repo: https://github.com/delexi/ng-test-fast-check-ie11

Steps to reproduce:

• Create an Angular 9 project: npx @angular/cli@9.1.12 new fast-check-ie (or use example repo)
• Enable differential loading and install fast-check and IE support for karma (or use example repo)
• Add a simple fast-check test (or use example repo)
• In project root run ng test --configuration=es5
• If you are quick to press F12 after IE starts up you can capture the syntax error in IE’s Console and navigate from there to the correct location in vendor.js mentioned above. Otherwise karma’s console output should mention the syntax error as well.

Expected behavior

I expect that adding fast-check to my angular tests does not break them in IE11.

Your environment

Packages / Softwares	Version(s)
fast-check	2.4.0
node	12.8.2
TypeScript	3.8.3

[delexi]

Actually, the workaround I was talking about happens to be in the thread I already mentioned. This and the following comment: https://github.com/angular/angular-cli/issues/9339#issuecomment-360213460. I haven’t actually tried these though.

[dubzzz]

No worry, I’ll have a look to your issue more precisely and try to come with a better and more sustainable fix.