javascript

CHAPTER 5 ■ MEMBER INHERITANCE
174
Figure 5–18. Adding members in prototypal inheritance
Cloning Members
Another way to clone an object is to do a deep copy of its members. Unlike emulate() shown earlier,
which does a shallow copy of members (that is, members of the object type are copied by reference), a
deep copy recursively clones those. Let’s write a helper function named cloneMembers() that will clone
an object by doing a deep copy of its members, deferring the explanation of recursion until Chapter 6.
var cloneMembers = function (donor, donee) {
donee = donee || {};
for (var m in donor) {
if (typeof donor[m] === "object" && donor[m] !== null) {
donee[m] = typeof donor[m].pop === "function" ? [] : {};
cloneMembers(donor[m], donee[m]);
} else {
donee[m] = donor[m];
}
}
return donee;
};
Now if we want to make a quart of Ben & Jerry’s Coffee Heath Bar Crunch from Vanilla Heath Bar
Crunch, we’d clone the latter by doing a deep copy of its members. Then add a coffee member, verifying
our work with Figure 5–19. Note that coffeeHeathBarCrunch does not inherit members from
vanillaHeathBarCrunch via the prototype chain. Rather, coffeeHeathBarCrunch has deep copies of
vanillaHeathBarCrunch members. So, no prototype chain this time.