This plugin is just a helper function for calculating a diff of two similar objects ala ActiveRecord's changes hash. Just pass in two objects and this function will return an object of changes that contains only the properties that have changed.
Usage:
var before = {id:123, name:{first:"Johnny", last:"Johnson"}};
var after = {id:123, name:{first:"John", last:"Johnson"}, age:30};
var changes = $.objectDiff(before, after);
Result (contents of changes):
{name: {first:"John"}, age:30}