js: object/array isEqual method

isequal.js

Object.prototype.isEqual = function(obj) {

  function iter(a, b) {
    for(p in a) {
      if(a.hasOwnProperty(p)) {

        if(!b.hasOwnProperty(p)) return false;

        else if(['array', 'object'].indexOf(typeof b[p]) > -1) {
          if(!iter(b[p], a[p])) return false;
        }

        else if(b[p] !== a[p]) return false;
      }
    }
    return true;
  }

  return iter(obj, this) && iter(this, obj);
}

mittens     = {color: 'white', age: 1, eyes: 'blue', sex: 'female', toys: ['yarn', 'catnip']}
furball     = {color: 'black', age: 2, eyes: 'yellow', sex: 'male', toys: ['mice', 'lizards']}
purrster    = {color: 'orange', age: 1, eyes: 'blue', sex: 'male', toys: ['boxes', 'shadows']}
blankinclaws = {color: 'brown', age: 21, eyes: 'brown', sex: 'male', toys: ['balls']}

a = {animals: [mittens, furball, purrster]}
b = {animals: [mittens, furball, purrster]}
c = {animals: [mittens, furball, purrster, blankinclaws ]}

a.isEqual(b) // true
b.isEqual(a) // true
c.isEqual(a) // false
a.isEqual(c) // false