JQuery создает многомерный массив на лету

var counter = 0;
var arr = [];
$('.unknown-number-of-elements').each(function(){
    var keyNumber = $(this).val();
    var valToPush = "foo"+counter;
    if (keyNumber in arr){
      arr[keyNumber].push(["'"+ valToPush +"'"]);
    }else{
      arr[keyNumber] = valToPush;
    }
    counter++;
});
console.info(arr);

<script src = "https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input class = "unknown-number-of-elements" value = "1">
<input class = "unknown-number-of-elements" value = "2">
<input class = "unknown-number-of-elements" value = "3">
<input class = "unknown-number-of-elements" value = "4">
<input class = "unknown-number-of-elements" value = "5">