like
dodge_feat = { 1, 'dodge' }
full_plate_mail = { 9, 'armor' }
mage_armor = { 4, 'armor' }

If you do, you can write a second array that only stores the value of each bonus that have the same name, then loop through this array looking for the highest integer, like this:
var array = [4 , 9, 1];
var highest= 0;
for (i=0; i<=highest;i++)
if (array[i]>highest)
var highest=array[i];

okay, here is what you want to do:
first write a loop that goes through your array, and for each different *type*, you save those that have the same name, then you call a second function that will check the highest between them.
secondly, this other function works like this:
{
var array = the array you just got from the first function;
var highest= 0;
var index_highest = 0;
for (i=0; i<=highest;i++)
if (array[i]['value']>highest) {
highest = array[i];
index_highest = i;
}
}

given that its an object with two properties, you could access it like this:
highest('armor')['name'] to obtain the name and highest('armor')['value'] to obtain the value.

it will output an object like this:

{ 'name': 'bonus name', 'value': 4 }

You dont have to, when you defined it's value, it became a string:
var name="";

and even if you didnt, when you used it inside your loop, the value it obtained was a string:
name=buffArray[i]['name'];

var newstring = name;

return newstring;

newstring will be contained within apostrophes.