Is there a function in Google Earth Engine (javascript) that can compare two lists against one list and storing the correct match in a new list?

Question

I need to compare two lists of items (a,b) to one list (c).
If a match is made, store it in a new list and If no match is found, keep the first list's label. Something like below-

if a = c, keep a. if a != c, look at b. if b = c, keep b. If b != c, keep a. 

I need this to run through each item in lists a and b.

Any help is appreciated thank you in advance.

I have only been able to compare one list to another list.