Simple deep equality comparison in Javascript (ES5+)

deepequal.js

// Deep Equality comparison example
//
// This is an example of how to implement an object-comparison function in 
// JavaScript (ES5+). A few points of interest here:
//
// * You can get an array of all an object's properties in ES5+ by calling
//   the class method Object.keys(obj). 
// * The function recursively calls itself in the for / in loop when it
//   compares the contents of each property
// * You can hide a "private" function inside a function of this kind by
//   placing one function declaration inside of another. The inner function
//   is not hoisted out into the global scope, so it is only visible inside
//   of the parent function.
// * The reason this nested helper function is necessary is that 
//   `typeof null` is still "object" in JS, a major "gotcha" to watch out for.
//
function deepEqual(obj1, obj2) {
  if (obj1 === obj2) {
    return true;
  } else if (isObject(obj1) && isObject(obj2)) {
    if (Object.keys(obj1).length !== Object.keys(obj2).length) { return false; }
    for (var prop in obj1) {
      if (!deepEqual(obj1[prop], obj2[prop])) {
        return false;
      }
    }
    return true;
  }

  // Private
  function isObject(obj) {
    if (typeof obj === "object" && obj != null) {
      return true;
    } else {
      return false;
    }
  }
}