Maintaining order of http requests within a for loop in javascript

Question

I am trying to save an array of objects in MongoDB using node.js express and mongoose (MEAN stack). However, when I make the http post requests on the front end for each item in the array, they don't show up on the back end in that order. Here's what I have on the front end:

$scope.postThenPost = function() {
    $http.post('/collection', $scope.doc).success(function(data){
        for (var i = 0; i<$scope.array.length; i++) {
            var req_obj = { thing: $scope.array[i] };
            $http.post('/collection2', req_obj);
        };
    };
};

and on the back end, express runs this for posting into /collection2:

exports.create = function(req, res) {
    var q = new q(req.body.thing);
    q.save(function(err) {
        if (err) {
            return res.status(400).send({
                message: errorHandler.getErrorMessage(err)
            });
        } else {
            res.jsonp(q);
        };
    });
};

Is there something I can do to ensure that the array goes in to the database in order? Thanks in advance

The $http.post is asynchonous by default. I recommend you posting the entire $scope.array to /collection2, then loop through the array on back end. — Huy Hoang Pham
– Huy Hoang Pham, Commented Jul 10, 2015 at 3:42

Matt Harrison · Accepted Answer · 2015-07-10 03:48:26Z

1

It's wasteful sending $scope.array.length number of HTTP requests when you have all the data you want to send ready.

Just post the whole array to your backend and then you can save them in a loop on the backend using something like async to guarantee the order.

answered Jul 10, 2015 at 3:48

Matt Harrison

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