Comparing Objects in JavaScript

Hi Guys,

Does anyone have a good method that can returns true if all values in one object match that in another object? (it needs to support recursion too)

Ex:
var o1 = {
  item1:123
  item2: {
    item3: 456
  }
}
var o2 = {
  item1:123
  item2: {
    item3: 456
  }
}
var o3 = {
  item1:123
  item2: {
    item3: 'ABC'
  }
}

So when comparing o1 to o2 the method would eval to true, comparing o1 to o3 would eval to false.

Cheers,
Dan
LVL 3
dancablamAsked:
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HonorGodSoftware EngineerCommented:
That might be difficult.  Consider the scenario where the object contains a "this" reference.
The eval would only be able to return true if the objects being compared refer to a single object.
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HonorGodSoftware EngineerCommented:
A simple test to see if two variables reference the same object would be to use the === operator.


function same( a, b ) {
  return a === b;
}

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dancablamAuthor Commented:
The objects will only contain data - not methods. Also they won't be referencing the same object so the === won't work. I simply need a method to walk recursively down an object and see if all the property/value combinations match.
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lanewayCommented:
This will work for objects that both have the same values:
function compareObj(obj1,obj2) {
    // if obj1 and obj2 are not both objects, return simple comparison
    if (typeof obj1 != 'object' || typeof obj2 != 'object') { return (obj1==obj2); }
    // compare indexes in obj1 with those in obj2
    for (index in obj1) {
      var item1 = obj1[index];
      var item2 = obj2[index];
      if (typeof item1 == 'object') if (!compareObj(item1,item2)) return false;
      if (typeof item1 != 'object') if (item1!=item2) return false;
    }
    // if we got this far, the are the same
    return true;
} 
 
// demo
var o1 = { item1:123, item2: { item3: 456 } };
var o2 = { item1:123, item2: { item3: 456 } };
var o3 = { item1:123, item2: { item3: 'ABC' } };
alert(compareObj(o1,o2));
alert(compareObj(o1,o3));

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lanewayCommented:
Clarification. The above code will work for objects that both have the same properties. Example:
// comparing these two will work
var o1 = { item1:'abc' }
var o2 = { item1:'def' }
// but comparing these two won't always work properly
var o1 = { item1:'abc' }
var o2 = { item1:'def',item2:'xyz' }

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HonorGodSoftware EngineerCommented:
Something like this perhaps?
<html>
<body>
 
<script type="text/javascript">
var o1 = {
  item1 : 123,
  item4 : 'Hi',
  item2 : { item3 : 456 }
}
var o2 = {
  item1 : 123,
  item4 : 'hi',
  item2 : { item3 : 456 }
}
var o3 = {
  item1 : 123,
  item4 : 'Hi',
  item2 : { item3 : 'ABC' }
}
 
function oCompare( o1, o2 ) {
  var result = false;
  if ( typeof( o1 ) == typeof( o2 ) ) {
    if ( typeof( o1 ) == 'object' ) {
      if ( o1 === o2 ) {
        return true;
      } else {
        for ( p in o1 ) {
          if ( p in o2 ) {
            var T = typeof( o1[ p ] );
            if ( T == typeof( o2[ p ] ) ) {
              switch ( T ) {
                case 'boolean' : if ( o1[ p ] != o2[ p ] ) return false;
                  break;
                case 'number' : if ( o1[ p ] != o2[ p ] ) return false;
                  break;
                case 'function' : if ( o1[ p ] !== o2[ p ] ) return false;
                  break;
                case 'string' : if ( o1[ p ] != o2[ p ] ) return false;
                  break;
                case 'object' : if ( !oCompare( o1[ p ], o2[ p ] ) ) return false;
                  break;
                default:
                  alert( 'p: ' + p + ' typeof: ' + T );
              }
            } else {
              return false;
            }
          } else {
            return false;
          }
        }
      }
    }
  }
  return result;
}
 
document.write( oCompare( o1, o3 ) );
 
</script>
 
</body>
</html>

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HonorGodSoftware EngineerCommented:
nope, not quite...

We also have to check that all properties in object2 exist and are the same as found in object1...
<html>
<body>
 
<script type="text/javascript">
var o1 = {
  item1 : 123,
  item4 : 'Hi',
  item2 : { item3 : 456 }
}
var o2 = {
  item1 : 123,
  item4 : 'Hi',
//item5 : true,
  item2 : { item3 : 456 }
}
var o3 = {
  item1 : 123,
  item4 : 'Hi',
  item2 : { item3 : 'ABC' }
}
 
function oCompare( o1, o2 ) {
  if ( typeof( o1 ) == typeof( o2 ) ) {
    if ( typeof( o1 ) == 'object' ) {
      if ( o1 === o2 ) {
        return true;
      } else {
        for ( p in o1 ) {
          if ( p in o2 ) {
            var T = typeof( o1[ p ] );
//          alert( p + ' ' + o1[ p ] + ' ' + o2[ p ] );
            if ( T == typeof( o2[ p ] ) ) {
              switch ( T ) {
                case 'boolean' : if ( o1[ p ] != o2[ p ] ) return false;
                  break;
                case 'number' : if ( o1[ p ] != o2[ p ] ) return false;
                  break;
                case 'function' : if ( o1[ p ] !== o2[ p ] ) return false;
                  break;
                case 'string' : if ( o1[ p ] != o2[ p ] ) return false;
                  break;
                case 'object' : if ( !oCompare( o1[ p ], o2[ p ] ) ) return false;
                  break;
                default:
//                alert( 'p: ' + p + ' typeof: ' + T );
              }
            } else {
              return false;
            }
          } else {
            return false;
          }
        }
      }
    }
  }
  return true;
}
 
document.write( oCompare( o1, o2 ) && oCompare( o2, o1 ) );
 
</script>
 
</body>
</html>

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HonorGodSoftware EngineerCommented:
Thanks for accepting my solution.

I'm sorry that you didn't feel that it was worthy of an A.

Good luck & have a great day.
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