error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
  Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
tests/cases/compiler/a.js(2,8): error TS8009: The '?' modifier can only be used in TypeScript files.
tests/cases/compiler/a.js(4,8): error TS8009: The '?' modifier can only be used in TypeScript files.


!!! error TS5055: Cannot write file 'tests/cases/compiler/a.js' because it would overwrite input file.
!!! error TS5055:   Adding a tsconfig.json file will help organize projects that contain both TypeScript and JavaScript files. Learn more at https://aka.ms/tsconfig.
==== tests/cases/compiler/a.js (2 errors) ====
    class C {
        foo?() {
           ~
!!! error TS8009: The '?' modifier can only be used in TypeScript files.
        }
        bar? = 1; 
           ~
!!! error TS8009: The '?' modifier can only be used in TypeScript files.
    }