Typeahead modifies Observable prototype

Bug description:

The current code modifies the prototype of Observable in the typeahead component using statements like here:

https://github.com/ng-bootstrap/ng-bootstrap/blob/cfbc24a020d17b17181e684575df915d82e44a26/src/typeahead/typeahead.ts#L21

import 'rxjs/add/observable/fromEvent';

This is bad for several reasons. The consuming application is not aware of what is imported where and under which conditions. Also it constitutes a side effect which is generally to be avoided. The right way to do it is to import the operator as a function and use it standalone (e.g. map.call(myObservable, ...)), passing the Observable as an argument. An example can be found in the Angular code base:

https://github.com/angular/angular/blob/master/modules/%40angular/router/src/router.ts#L20

https://github.com/angular/angular/blob/master/modules/%40angular/router/src/router.ts#L685

[DzmitryShylovich]

The fix is very simple and ng-bootstrap only has it in one component so if you prefer I could try my luck with a PR…

it’s not true https://github.com/ng-bootstrap/ng-bootstrap/search?utf8=✓&q=rxjs%2Fadd%2Fobservable

[DzmitryShylovich]

@blesh thx 😃