nextUp(); getting next higher permutation of number

nextup.js

// Given a number, find the next higher number which has the exact same set of digits as the original number
// http://stackoverflow.com/questions/9368205/given-a-number-find-the-next-higher-number-which-has-the-exact-same-set-of-digi

function nextUp(iNumber){

	var sDigitsSorted = iNumber.toString().split('').sort().join('');

	var aPermutations = (function(){
		var i = parseInt(iNumber.toString().split('').sort().reverse().join(''),10) + 1,
			a = [];
		// this is crazy inefficient
		while (i--) {
			var sSorted = i.toString().split('').sort().join('');
			if (sSorted.length !== sDigitsSorted.length) { break; }
			if (sSorted === sDigitsSorted) { a.push(i); }
		}
		return a.sort();
	}());

	return (function(){
		var iCount = aPermutations.length;
		for (var i=0; i<iCount; i++){
			var iPermutation = aPermutations[i];
			if (iPermutation > iNumber) {
				return iPermutation;
			}
		}
		return null;
	}());

}

That iterator smells really inefficient, but it works. Hmmm.....