Input a number Output the next largest number using the same combination of numbers.

PermutationStep

function PermutationStep(num) { 
	var numString = num.toString();
	var numArray = numString.split("")

	var numArrayStart = [];
	var numArrayEnd = [];

	for (var i = numArray.length-1; i>0; i--) {
		if(Number(numArray[i])<Number(numArray[i+1])){
			numArrayStart.push(numString.substring(0,i))
			numArrayEnd.push(numString.substring(i,numString.length));
			break;
		}
	}
	if(numArrayEnd[0]===undefined){
		alert("a larger number with the same number combination does not exist");
	}
	var endSplitArray = numArrayEnd[0].split("");
	var breakNumber = Number(endSplitArray[0]);
	var endSplitArraySort = endSplitArray.sort();

	for (var i = 0; i < endSplitArray.length; i++) {
		if(Number(endSplitArray[i])>breakNumber){
			numArrayStart.push(endSplitArray[i]);
			endSplitArray.splice(i,1);
			break;
		}
	}
	var endSplitArrayRev = endSplitArray.join("").toString();
	numArrayStart.push(endSplitArrayRev);
	var output = Number(numArrayStart.join(""));
	return output;
}

console.log("6345634563456=", PermutationStep(6345634563456));