[cyber]

так?

Array.prototype.compare = function(arr) {
    
    var search = arr.slice(),
        remove = [];
    
    for(var i = 0, index; i < this.length; i++) {
        
        index = search.indexOf(this[i]);

		if(!~index) {
          
			remove.push(this[i]);
            
            continue;
        }
        
        delete search[index];

	};
    
    return {
        remove: remove,
        insert: search
    }
    
}

console.log([1,2,3,4].compare([2,3,4,5, 34, 2 , 3434]));