When webpack bundles your javascript it wraps all of your individual files/modules in functions so they are no longer run in the global scope, therefore if you want to make a variable global you have to explicitly set it on the window object, i.e.
window.a = 1;
@startuml
participant User
User -> A: DoWork
activate A #FFBBBB
A -> A: Internal call
activate A #DarkSalmon
A -> B: << createRequest >>
activate B
B --> A: RequestCreated
deactivate B
deactivate A
A -> User: Done
deactivate A
@enduml