How can I do reverse in a for loop?

Question

I have this Js method but I can't to implement a reverse loop

$scope.organizeByMonth = function () {    
    for (var i in $scope.incidents) {

        var month = new Date($scope.incidents[i].upload_date).getMonth();    
        if (!monthIncidents[month]) {

            monthIncidents[month] = {    
                name: $scope.months[month],
                incidents: []
            };
        }
        var incident = $scope.incidents[i];    
        incident.index = i;    
        monthIncidents[month].incidents.push(incident);
    }
};

how can I show the same objects in reverse :/

See http://stackoverflow.com/questions/500504/why-is-using-for-in-with-array-iteration-such-a-bad-idea if $scope.incidents is an array (which it looks like it is because `push` is used for a similar name). If it is an array it can be easily reversed prior to iterating it; or the 'explicit for' form can be trivially used. — user2864740, Jul 20 '15 at 21:12

score 3 · Answer 1 · answered Jul 20 '15 at 21:09

3

You can't do a reverse loop with the for in syntax - it also doesn't matter. Objects in JavaScript are unordered.

answered Jul 20 '15 at 21:09

tymeJV

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And maybe more to the point: the code is *probably* incorrectly using `for..in` for an array. – user2864740 Jul 20 '15 at 21:11

score 1 · Answer 2 · answered Jul 20 '15 at 21:12

1

The closest to a reverse for..in.. loop would be to get the object keys and iterate backwards over them:

var object = { a: 1, b: 2, c: 3 };
var keys = Object.keys(object);
for(var i = keys.length - 1; i >= 0; i--) {
    console.log(keys[i], object[keys[i]]);
}

http://jsfiddle.net/1oztmp2e/

answered Jul 20 '15 at 21:12

Sebastian Nette

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Won't matter for an object, they're unordered! – tymeJV Jul 20 '15 at 21:14
Nothing stops you from ordering the keys with a sort call. It entirely depends on the OP and how he intends to use it. – Sebastian Nette Jul 20 '15 at 21:15
You can't sort the keys, it could be interpreted differently depending on the browser. – tymeJV Jul 20 '15 at 21:16
Ofcourse you can. If we both refer to `var keys = Object.keys(object);` – Sebastian Nette Jul 20 '15 at 21:18
http://stackoverflow.com/questions/5525795/does-javascript-guarantee-object-property-order – tymeJV Jul 20 '15 at 21:19
Again: `var keys = Object.keys(object);` is an array and arrays can be sorted. – Sebastian Nette Jul 20 '15 at 21:19
Ahh - yeah, you can sort the keys - I was talking about the object itself – tymeJV Jul 20 '15 at 21:20
Yes, that's why I edited it in my prior comment but you were too fast replying :P – Sebastian Nette Jul 20 '15 at 21:20

score 0 · Answer 3 · edited May 23 '17 at 11:58

0

Why would you like to reverse the for loop? Is it only for display purpose?

If so, I am assuming you are using ng-repeat for displaying the records. Should that be the case, you can use a custom reverse filter.

Or if you need the array reversed for a different reason, simply use Array.reverse after populating the array

edited May 23 '17 at 11:58

Community

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answered Jul 20 '15 at 21:16

Michele Ricciardi

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How can I do reverse in a for loop?

3 Answers3