deepEquality.js

/**
  * Write a function that, given two objects, returns whether or not the two
  * are deeply equivalent--meaning the structure of the two objects is the
  * same, and so is the structure of each of their corresponding descendants.
  *
  * Examples:
  *
  * deepEquals({a:1, b: {c:3}},{a:1, b: {c:3}}); // true
  * deepEquals({a:1, b: {c:5}},{a:1, b: {c:6}}); // false
  *
  * don't worry about handling cyclical object structures.
  *
  
  NOTE: if your interviewee immediately jumps to a JSON.stringify-based solution, acknowledge that it is a 
  naive & valid implementation but add it as a constraint to NOT use it for their solution. 
  */

// Solution
 
var deepEquals = function(apple, orange) {

  if (apple === orange) { return true; }
  if (apple && !orange || !apple && orange) { return false; }
  if (!(apple instanceof Object) || !(orange instanceof Object)) { return false; }
  var appleKeys = Object.keys(apple);
  var orangeKeys = Object.keys(orange);
  if (appleKeys.length !== orangeKeys.length) { return false; }
  if (appleKeys.length === 0) { return true; } // two empty objects are equal
  for (var i = 0; i < appleKeys.length; i++) {
    if (!deepEquals(apple[appleKeys[i]], orange[appleKeys[i]])) { return false; }
  }
  return true;
};