$anchorScroll goes to wrong point if dynamically changing element position to fixed

Question

I'm using a directive to fix my menu to the top of the page once my header scrolls past. I also would like my menu to use $anchorScroll to navigate to different elements of the page. The trouble I'm having is that the $anchorScroll goes past the anchor point unless you have scrolled past the header.

var myApp = angular.module('myApp', ['sticky']);

    function IndexCtrl($scope, $location, $anchorScroll) {
    $scope.gotoDiv = function (id) {
        $scope.id = id;
        $location.hash(id);
        $anchorScroll();
    }
}

angular.module('sticky', [])
.directive('sticky', [ function () {
    return {
        restrict: 'A',

        link: function ($scope, $elem, $attrs) {
            var offsetTop = 0,
                $window = angular.element(window),
                initialPositionStyle = $elem.css('position'),
                stickyLine,
                scrollTop;

            // Set the top offset
            $elem.css('top', '0');
            $window.on('scroll', checkSticky);
            setInitial();

            function setInitial() {
                stickyLine = $elem[0].offsetTop;
                checkSticky();
            }

            function checkSticky() {
                scrollTop = window.pageYOffset;
                if (scrollTop >= stickyLine) {
                    $elem.css('position', 'fixed');
                } else {
                $elem.css('position', initialPositionStyle);
                }
            }
        }
    };
}]);

I created this plunker: http://plnkr.co/edit/7HfPtu4f1VoQ5vz4yVOJ?p=preview

-Click the menu the first time, the scroll goes to far. -A second click takes you the correct position. -scroll past the header, then click scroll goes to the correct position.

Answer 1

The header needs to be set to fixed before the scroll happens. like this:

var myApp = angular.module('myApp', ['sticky']);

function IndexCtrl($scope, $location, $anchorScroll) {
    $scope.gotoDiv = function (id) {
      $scope.stickyHeader();
      $scope.id = id;
      $location.hash(id);
      $anchorScroll();
    }

    $scope.stickyHeader = function () {
      service001.elem.css('position', 'fixed');
    }
}

var service001 = {

}

angular.module('sticky', [])
    .directive('sticky', [ function () {
        return {
            restrict: 'A',

            link: function ($scope, $elem, $attrs) {
                var offsetTop = 0,
                    $window = angular.element(window),
                    initialPositionStyle = $elem.css('position'),
                    stickyLine,
                    scrollTop;

                // Set the top offset
                $elem.css('top', '0');
                $window.on('scroll', checkSticky);
                setInitial();

                service001.elem = $elem;

                function setInitial() {
                    stickyLine = $elem[0].offsetTop;
                    checkSticky();
                }

                function checkSticky() {
                    scrollTop = window.pageYOffset;
                    if (scrollTop >= stickyLine) {
                      $elem.css('position', 'fixed');
                    } else {
                      $elem.css('position', initialPositionStyle);
                    }
                }
            }
        };
    }]);

There should be a service in here to share the elem.css position, but there it is.