[ZackMercury]

var array:Array = [];
for(var j:int = 1; j <= 100; j ++)
array.push(j);
trace(array);
array.splice(array.indexOf(10));
for(var i:int = 1; i <= array.length + 1; i++)
{
if(array.indexOf(i) < 0) trace(i); //выводит 10
}

Сек, ошибся с функцией.
Хотя нет, не ошибся. Просто забыл передать второй параметр 1.

var array:Array = [];
for(var j:int = 1; j <= 100; j ++)
	array.push(j);
 
trace(array);
 
array.splice(array.indexOf(10),1);
 
trace(array);
 
for(var i:int = 1; i <= array.length + 1; i++)
{
   if(array.indexOf(i) < 0) trace(i); 
}

1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100

1,2,3,4,5,6,7,8,9,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100

10