To remove array elements from the lefthand side of an array one at a time, use shift. To do the same from the righthand side, use pop. If you need to add or remove one or more elements from anywhere in the array, use splice. As you've discovered, delete just undefines the value. splice can actually remove the elements and shift all subsequent elements up into place.

However, keep in mind that every time you call splice to remove elements from the middle of an array, you're performing an O(n) operation. If it's a large enough array, and you do it often enough, you might consider rethinking your algorithm. A hash would provide O(1) adds and deletes, though you would lose all notion of sortedness (and it would be silly to eliminate an O(n) operation and trade it for a O(n log n) sort).