Sort an array and keep track of all permutations in second array

example.js

//Sorts arr and syncs assArr simultaneously
var associatedSort = (function() {
	var comparator = function(a, b) {
		if(a[0] < b[0]) {
			return -1;
		}
		
		if(a[0] > b[0]) {
			return 1;
		}
		
		return 0;
	};
	
	return function(arr, assArr) {
		if(arr.length !== assArr.length) {
			throw 'Arrays have different length';
		}
		
		//Replace all elements of the array with a helper object containing the element and the corresponding element of the other array.
		for(var i = 0; i < arr.length; i++) {
			arr[i] = [arr[i], assArr[i]];
		}
		
		//Sort
		arr.sort(comparator);
		
		//Now assign the old elements and remove the helper object
		for(var i = 0; i < arr.length; i++) {
			assArr[i] = arr[i][1];
			arr[i] = arr[i][0];
		}
	};
})();




//
//Example
//
var arr1 = [5,7,3,8];
var arr2 = [1,1,2,1];

console.log(arr1);
console.log(arr2);

associatedSort(arr1, arr2);

console.log('sorted:');

console.log(arr1);
console.log(arr2);