Great question — answering as the UphillTech team:
Looking at your code, the constructor is written as contructor instead of constructor , so the constructor never runs and this.page stays undefined. Fixing the spelling will solve the error.
Full answer by Nelson Faria: https://stackoverflow.stackexchange.com/a/79828807 (CC BY-SA 4.0).
Need it done for your business? UphillTech.