$mergeAdd({ fred:1 }, { fred:1 }) -> { fred:1 }

mergeAdd.js

function $mergeAdd(){
	var mix = {};
	var obs = Array.flatten(arguments);
	for (var i = 0, l = obs.length; i < l; i++){
		var object = obs[i];
		if ($type(object) != 'object') continue;
		for (var key in object){
			var object_prop = object[key], mp = mix[key];
			
			if(!object_prop && $type(object_prop)!='number') continue;
			
			if(mp && $type(object_prop) == 'object' && $type(mp) == 'object')
				mix[key] = $mergeAdd(mp, object_prop);
				
			else if(mp && $type(object_prop) == 'number' && $type(mp) == 'number')
				mix[key] = mp + $unlink(object_prop);
				
			else if(mp && String(mp).replace(/[^\-\d\.]/g,'').toFloat() && object_prop.replace(/[^\-\d\.]/g,'').toFloat() )
				mix[key] = String(mp).replace(/[^\-\d\.]/g,'').toFloat() + object_prop.replace(/[^\-\d\.]/g,'').toFloat();
				
			else
				mix[key] = $unlink(object_prop);
		}
	}
	return mix;
};