How to pass Twine Story Variables to a Javascript Function?

I am using Sugarcube 2.6.2 in Twine 2.

So I figured it's about time I tackled that elephant in my IDE.
I've been researching into Javascript syntax recently because I want to figure out how to add a javascript function to my story, but now my issue lies in the interaction between twine and javascript.
I don't have any experience with combining code of different languages, so I'm a bit lost and most posts I've looked at relating to it are coming up greek to me.

So, my questions are thusly:
1) For example's sake, let's say I want to add a function that does something like the following pseudocode:

function foo($myStoryVariableObject) {
    if $myStoryVariableObject.name == "Jeremy" {
        print("The evil wizard transforms Jeremy into a chicken!")
        $myStoryVariableObject.status = "polymorphed"
    }
    else
    {
        print("Candy uses one of her spell slots to counter the wizard's spell!")
        $myStoryVariableObject.spellSlots = $myStoryVariableObject.spellSlots - 1
    }
}

How would I code this? More specifically, how do I send a story variable to javascript and access it within javascript? Are there any interactions/bugs/differences between Story objects and javascript objects that I should be aware of?

2) How do I call a javascript function in Twine 2? Again, for example's sake, let's say I call the above function, "foo", in this passage below:

The evil wizard waves his hands and chants arcane words! Your prepare to roll out of the way, but he aims at your companion! 
<<foo($companion)>>

What would be the correct way of calling the function?