How to use the prosemirror-transform.replaceStep function in prosemirror-transform

handleKeyDown: function (view, event) {
      if (event.code === 'Backspace') {
        const sel = view.state.selection;
        const pos = sel.$from;
        let tr = view.state.tr;
        // what if they delete a region??
        const beforeSel = Selection.findFrom(view.state.doc.resolve(sel.from - 1), -1, true);
        const marks = beforeSel.$from.marks();
        const hasDiff = marks.find((mark) => {
          return (mark.type.name === 'diff_plus');
        });
        const deleteStep = replaceStep(tr.doc, beforeSel.from, sel.from, Slice.empty);
        if (hasDiff) {
          // need to actually delete it but then avoid random deletions
          this.storeStep(deleteStep);
          tr.step(deleteStep);
          tr.setMeta('backdelete', true);
          view.dispatch(tr);
          return true;
        }
        // is this step size always 1??
        const newOffset = { index: beforeSel.from, size: 1 };
        this.storeStep(deleteStep);
        this.stepOffsets.push(newOffset);
        this.storeOffset(newOffset);

        tr = tr.addMark(beforeSel.from, sel.from, schema.mark('diff_minus', { commitID: this.tracker.uuid }));
        tr = tr.setSelection(beforeSel);

}
              }


              if (isSpaceOperation) {
                tr = tr.addMark(newStart, newEnd, schema.mark('diff_plus', { commitID: this.tracker.uuid  }));
                return;
              }


              tr = tr.step(inverse);
              const slice = step.slice.content;
              const possibleInsert = tr.mapping.map(newEnd, 1);

              if (step.slice.size > 0) {
                const insertstep = replaceStep(oldState.doc, possibleInsert, possibleInsert, (step.slice.size > 0) ? step.slice : Slice.empty);
                const newOffset = { index: oldEnd, size: inverse.slice.size };
                this.stepOffsets.push(newOffset);
                this.storeOffset(newOffset);
                try {
                  tr = tr.step(insertstep);
                } catch (err) {
                  console.log('cannot do this!', insertstep, step);
                  console.log(err);
                }
                tr = tr.addMark(oldStart, oldEnd, schema.mark('diff_minus', { commitID: this.tracker.uuid  }));
                const insertStart = tr.mapping.map(newEnd, -1);
                const insertEnd = tr.mapping.map(newEnd, 1);
                tr = tr.addMark(insertStart, insertEnd, schema.mark('diff_plus', { commitID: this.tracker.uuid  }));
              } else {
                const insertStart = tr.mapping.map(newEnd, -1);
                const insertEnd = tr.mapping.map(newEnd, 1);