Vanilla JavaScript: How to access functions with buttons, and how to access variables?

[Bishiba92]

Installed the app on my iphone today to perform a quick little statistical evaluation. Altough as the title implies, I have a button that uses onclick="endYear()", however, when I click this, it simply states that the endYear variable can't be found. I've been trying various ways to correct this, and I've also noticed that I can make it work in other applications, such as JSAnywhere on the iphone. JSAnywhere is quite barebones though, but can be useful.

So, this is how it looks:

Hitting the End Year button causes this:

I believe this may be caused by strict mode(?), but I am unsure.

Any help is appreciated!