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 
expect(newData.ref).toEqual(Ref.get(2, 0));
          oldData.data = oldData.data.replace(/\(D:[0-9]+\)/, "(date)");
          expect(oldData.data).toEqual(
            "123 0 obj\n" +
              "<< /Type /Annot /Subtype /Widget /FT /Tx /DA (/Helv 5 Tf) /DR " +
              "<< /Font << /Helv 314 0 R>>>> /Rect [0 0 32 10] " +
              "/V (hello world) /AP << /N 2 0 R>> /M (date)>>\nendobj\n"
          );
          expect(newData.data).toEqual(
            "2 0 obj\n<< /Length 77 /Subtype /Form /Resources " +
              "<< /Font << /Helv 314 0 R>>>> /BBox [0 0 32 10]>> stream\n" +
              "/Tx BMC q BT /Helv 5 Tf 1 0 0 1 0 0 Tm 2.00 2.00 Td (hello world) Tj " +
              "ET Q EMC\nendstream\nendobj\n"
          );
          done();
        }, done.fail);
    });
    it("should get field object for usage in JS sandbox", function (done) {
      const textWidgetRef = Ref.get(123, 0);
      const xDictRef = Ref.get(141, 0);
      const dDictRef = Ref.get(262, 0);
      const next0Ref = Ref.get(314, 0);
      const next1Ref = Ref.get(271, 0);
      const next2Ref = Ref.get(577, 0);
      const next00Ref = Ref.get(413, 0);
      const xDict = new Dict();
      const dDict = new Dict();
      const next0Dict = new Dict();
      const next1Dict = new Dict();
      const next2Dict = new Dict();