Choice / Session Storage

I had a little go at figuring out the session storage thing Tim told me about. What I'm trying to do is make it so the continue button only shows up once all three links have been clicked.

I tried adapting some examples from ws3schools....but they're quite obviously for a different purpose, I didn't think they'd work. I tried to look up examples of the same thing as I'm using it for but couldn't find any examples. My javascript skills are more using other people's functions and substituting my own data rather than writing my own from scratch.....

I then tried to make an extremely simple version from scratch, in a codepen here, which doesn't work, but I think it's just a case of the structure of the javascript not being quite right.... I will try a few more things out, then maybe just send it to Tim and ask if he can correct it because I think once I've got that working I should be able to adapt it to possible other things