Remapping for Chrome OS deadKey function

Question

I'm working on a remapping for Chrome OS but can't get the deadKey function work.

Part of my Code:

var dmg ={
"Digit2": { "plain": {"plain": "2", "shifted": """}, "alternate": {"plain": function () {return deadkey ("2")}, "shifted": function () {return deadKey("gr2")}, "code": "#N/A"},
};

var deadKeysCombos ={
"2": {"a":"ä", "A":"Ä", "e":"ë", "E":"Ë", "i":"ï", "I":"Ï", "o":"ö", "O":"Ö", "u":"ü", "U":"Ü", "y":"ÿ", "Y":"Ÿ", " ":"¨", "¨":"¨¨", }
};

I'm pretty new in JS so I can't really get any further myself and couldn't find anything. As a template I used a similar code as

https://github.com/google/extra-keyboards-for-chrome-os/blob/46a94cdaee9f4935f08444e053984415a521d471/bepo/beporemap/background.js