`arguments` Object in JavaScript

Question

Secrets of the JavaScript Ninja explains the arguments keyword with the merge() function:

function merge(root){
 for (var i = 1; i < arguments.length; i++) { // starts at i = 1, not 0
   for (var key in arguments[i]) {
     root[key] = arguments[i][key];
   }
 }
 return root;
}

var merged = merge(
 {name: "Batou"},
 {city: "Niihama"});

Note the assertions:

assert(merged.name == "Batou", 
    "The original name is intact.");
assert(merged.city == "Niihama", 
    "And the city has been copied over.");

Why does merged.name equal Batou rather than undefined?

Since, as I understand, merge() does not look at the first argument in the outer for-loop, how does the name: Batou get added to root?

Answer 1

root itself is the first argument, thus we don't need to add whatever members is in it to itself.

Answer 2

It's already in root. That's the first parameter