Question: If I have two associative arrays, what would be the most efficient way of doing a diff against their values?

For example, given:

```
  array1 = {
    foreground: 'red',
    shape: 'circle',
    background: 'yellow'
  };

  array2 = {
    foreground: 'red',
    shape: 'square',
    angle: '90',
    background: 'yellow'
  };

```

How would I check one against the other, such that the items *missing* **or** *additional* are the resulting array. In this case, if I wanted to compare array1 within array2, it would return:

```
array3 = {shape: 'circle'}

```

Whilst if I compared array2 within array1, it would return:

```
array3 = {shape: 'square', angle: '90'}

```

Thanks in advance for your help!

Answer: 
If you're familiar with PHP syntax, take a look at <http://phpjs.org/functions/index> which includes almost all PHP's array related functions converted into JavaScript – including [`array_diff`](http://phpjs.org/functions/array_diff:309)
RaYell's solution is nice but unfortunately will only tell you the items in obj2 that are either different from or non-existant in obj1, if we need to know both sides, let's get all keys and then compare. The following function will return an associative array with key values for each object. Oh... to be fair, I haven't tested yet, but this should work.

```
var diff = function(obj1,obj2) {
  var newObj = $.extend({},obj1,obj2);
  var result = {};
  $.each(newObj, function (key, value) {
      if (!obj2.hasOwnProperty(key) || !obj1.hasOwnProperty(key) || obj2[key] !== obj1[key]) {
         result[key] = [obj1[key],obj2[key]];
      }
  });

  return result;
}

```

Oh, and while I do recognize that the first solution answered the initial question, I think the above solution offers another approach that the initial user might find useful so as to not require checking twice.