Comparing two potential ways to solve the "attach a 'global' function to my Angular app" question

factory_method.js

myApp.factory('queryStringFactory', [function() {
    return function(obj) {
        var params = []

        for (var key in obj) {
            params.push(
                encodeURIComponent(key) + '=' + encodeURIComponent(obj[key])
            )
        }

        return params.join('&')
    }
}])

myApp.controller('linkerCtrl', ['$scope', 'queryStringFactory', function($s, qs) {
    $s.getLink = function() {
        return 'some-page.html?' + qs({
            key1: $s.someModel.key1,
            key2: $s.someModel.key2
        })
    }
}])

object_method.js

myApp.queryString = function(obj) {
    var params = []

    for (var key in obj) {
        params.push(
            encodeURIComponent(key) + '=' + encodeURIComponent(obj[key])
        )
    }

    return params.join('&')
}

myApp.controller('linkerCtrl', ['$scope', function($s) {
    $s.getLink = function() {
        return 'some-page.html?' + myApp.queryString({
            key1: $s.someModel.key1,
            key2: $s.someModel.key2
        })
    }
}])