code: function diff( a, b ) {
  	var result = a.slice();
  	for ( var i = 0; i < result.length; i++ ) {
  		for ( var j = 0; j < b.length; j++ ) {
  			if ( result[i] === b[j] ) {
  				result.splice(i, 1);
  				i--;
  				break;
  			}
  		}
  	}
  	return result;
  }
docs: returns a new Array with the elements that are in a but not in b