You stumbled upon someone's "JS Safe" on the web. It's a simple HTML file that can store secrets in the browser's localStorage. This means that you won't be able to extract any secret from it (the secrets are on the computer of the owner), but it looks like it was hand-crafted to work only with the password of the owner...

https://storage.googleapis.com/gctf-2018-attachments/4dead099e841668a8d86e36fcde8099ce134c195da9863dfb9039043d366942d