Object equality

object_equality.js

/*
deepEquals tests two objects and returns true if:
- both objects are === identical
- both objects are NaN
- both objects are arrays, and at each index, the values are deepEquals (recursively)
- both objects have the same prototype, the same keys, and at each key, the values are deepEquals (recursively)
- a function reference is compared to another reference to the same function

deepEquals returns false if:
- two objects have the same keys and values, but were created with different constructors
- two arrays have the same values in a different order
- a function is compared with another function, even if they have identical declarations

Examples:
deepEquals("foo", "foo")                                    // true
deepEquals("foo", "bar")                                    // false
deepEquals(Infinity, Infinity)                              // true
deepEquals([], [])                                          // true
deepEquals({}, {})                                          // true
deepEquals([0, 1, 2], [0, 1, 2])                            // true
deepEquals([0, 1, 2], [2, 1, 0])                            // false
deepEquals({ a: 'b', 'b': a }, { a: 'b', b: 'a' })          // true
deepEquals({ a: 'b', 'b': a }, { b: 'a', a: 'b' })          // true
deepEquals({ a: { b: { c: 'd' }}}, { a: { b: { c: 'd' })    // true
deepEquals([0, { a: 'b', b: 'a' }], [0, { b: 'a', a: 'b' }) // true

var f = function() { return; };
var g = f;
deepEquals(f, g)                                            // true
deepEquals(f, function() { return; })                       // false

var Car = function() {
  this.make = 'Ford';
  return this;
}

var Truck = function() {
  this.make = 'Ford';
  return this;
}

var car = new Car();
var truck = new Truck();
deepEquals(car, truck) // false
*/

function deepEquals(thing1, thing2) {
  if (thing1 === thing2) {
    return true;
  } else if (Number.isNaN(thing1) && Number.isNaN(thing2)) {
    return true;
  } else if (Array.isArray(thing1) && Array.isArray(thing2)) {
    return arraysEqual(thing1, thing2);
  } else if (typeof(thing1) === 'object' && typeof(thing2) === 'object') {
    return objectsEqual(thing1, thing2);
  } else {
    return false;
  }
}

function arraysEqual(array1, array2) {
  if (array1.length !== array2.length) {
    return false;
  } else {
    return array1.every(function(item, index) {
      return deepEquals(array1[index], array2[index]);
    });
  }
}

function objectsEqual(obj1, obj2) {
  if (obj1.constructor !== obj2.constructor) {
    return false;
  }
  var obj1Keys = Object.keys(obj1);
  var obj2Keys = Object.keys(obj2);
  if (!arraysEqual(obj1Keys.sort(), obj2Keys.sort())) {
    return false;
  }
  return obj1Keys.every(function(key) {
    return deepEquals(obj1[key], obj2[key]);
  });
}