In the following spots a "MouseUp" eventName is being used, which does look inconsistent considering that the "Mouse Down"/"Mouse Enter"/"Mouse Exit" eventNames all have a space in them.
Is this inconsistency actually expected, or is it a simple typo? If the former, then a comment explaining *why* would be appropriate; otherwise we should just fix this :-)

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L806

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L945

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1034

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1168

/cc @calixteman 
next2Dict.set("S", JS);
      dDict.set("JS", "bar()");
      dDict.set("S", JS);
      dDict.set("Next", dDictRef);
      additionalActionsDict.set("D", dDictRef);
      additionalActionsDict.set("X", xDictRef);
      textWidgetDict.set("AA", additionalActionsDict);
      partialEvaluator.xref = xref;
      AnnotationFactory.create(
        xref,
        textWidgetRef,
        pdfManagerMock,
        idFactoryMock
      )
        .then(annotation => {
          return annotation.getFieldObject();
        })
        .then(object => {
          const actions = object.actions;
          expect(actions.MouseEnter).toEqual(["hello()"]);
          expect(actions.MouseExit).toEqual([
            "world()",
            "olleh()",
            "foo()",
            "dlrow()",
            "oof()",
          ]);
          expect(actions.MouseDown).toEqual(["bar()"]);
          done();
        }, done.fail);