AngularJS: Best way to watch dimensions?

Question

So, I\'ve come up with a few solutions to this and I\'m still not quite sure what is best. First for reference there is one similar question I could find, though it\'s a bit ol

Answer 1

Unfortunately this question didn't get as much attention as I would have liked... And I don't have time to write a detailed explanation with background, profiler screenshots, etc. But I did find a solution, and I hope this helps someone else dealing with the same issue.

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Conclusion

The $digest loop in any realistic medium-large application will not be able to handle a refresh of 100ms.

Given the requirement of setInterval I simply bypassed the loop entirely, instead opting to broadcast a state change only when differing dimensions are detected (using the offsetWidth/Height native properties).

Running at a 100ms interval with a single $root scope manifest is giving the best results of anything I've tested, with ~10.2% active-tab CPU on my 2.4Ghz i7 2013 MBP--acceptable compared to the ~84% with $interval.

Any comments and critiques are welcome, otherwise, here is the self-contained directive! Obviously you can get creative with the scope and/or attributes to customize the watchers, but in the interest of staying on topic I've tried to omit any superfluous code.

It will monitor & bind size changes on an element to a scope property of your choosing, for N elements with a linear complexity. I can't guarantee it's the fastest/best way to do this, but it's the fastest implementation I could develop quickly that tracks state-agnostic DOM-level dimension changes:

app.directive('ngSize', ['$rootScope', function($root) {
  return {
    scope: {
        size: '=ngSize'
    },
    link: function($scope, element, attrs) {

        $root.ngSizeDimensions  = (angular.isArray($root.ngSizeDimensions)) ? $root.ngSizeDimensions : [];
        $root.ngSizeWatch       = (angular.isArray($root.ngSizeWatch)) ? $root.ngSizeWatch : [];

        var handler = function() {
            angular.forEach($root.ngSizeWatch, function(el, i) {
                // Dimensions Not Equal?
                if ($root.ngSizeDimensions[i][0] != el.offsetWidth || $root.ngSizeDimensions[i][1] != el.offsetHeight) {
                    // Update Them
                    $root.ngSizeDimensions[i] = [el.offsetWidth, el.offsetHeight];
                    // Update Scope?
                    $root.$broadcast('size::changed', i);
                }
            });
        };

        // Add Element to Chain?
        var exists = false;
        angular.forEach($root.ngSizeWatch, function(el, i) { if (el === element[0]) exists = i });

        // Ok.
        if (exists === false) {
            $root.ngSizeWatch.push(element[0]);
            $root.ngSizeDimensions.push([element[0].offsetWidth, element[0].offsetHeight]);
            exists = $root.ngSizeWatch.length-1;
        }

        // Update Scope?
        $scope.$on('size::changed', function(event, i) {
            // Relevant to the element attached to *this* directive
            if (i === exists) {
                $scope.size = {
                    width: $root.ngSizeDimensions[i][0],
                    height: $root.ngSizeDimensions[i][1]
                };
            }
        });

        // Refresh: 100ms
        if (!window.ngSizeHandler) window.ngSizeHandler = setInterval(handler, 100);

        // Window Resize?
        // angular.element(window).on('resize', handler);

    }
  };
}]);