deepComparison.js

/*Deep comparison*/

/*
The == operator compares objects by identity. But sometimes, you would prefer to compare the values of their actual 
properties.

Write a function, deepEqual, that takes two values and returns true only if they are the same value or are objects with 
the same properties whose values are also equal when compared with a recursive call to deepEqual.

To find out whether to compare two things by identity (use the === operator for that) or by looking at their 
properties, you can use the typeof operator. If it produces "object" for both values, you should do a deep comparison. 
But you have to take one silly exception into account: by a historical accident, typeof null also produces "object".
*/

function deepEqual(obj1, obj2) {
  if ((typeof obj1 == "object" && obj1 != null) && (typeof obj2 == "object" && obj2 != null)) {
    if (Object.keys(obj1).length != Object.keys(obj2).length) return false;
    else {
      for (var prop in obj1) {
        if (obj2.hasOwnProperty(prop)) {
          return (deepEqual(obj1[prop], obj2[prop])) ? true : false;
        }
      }
    }
  }
  else {
    return (obj1 === obj2) ? true : false;
  }
}

var obj = {here: {is: "an"}, object: 2};
console.log(deepEqual(obj, obj));
// → true
console.log(deepEqual(obj, {here: 1, object: 2}));
// → false
console.log(deepEqual(obj, {here: {is: "an"}, object: 2}));
// → true