What steps can I take to guarantee that a directive's link function is executed prior to a controller?

Question

What steps can I take to guarantee that a directive's link function is executed prior to a controller?

Our application features a view that is loaded through a basic route setup.

$routeProvider
    .when('/', {
        template: require('./views/main.tpl.html'),
        controller: 'mainCtrl'
    })
    .otherwise({
        redirectTo: '/'
    });

This configuration links the mainCtrl controller to the view, which contains the following structure:

<left-rail>
    <filter-sub-rail
        id="filter-rail"
        show-all-filter="isAdmin"
        components="components">
    </filter-sub-rail>
</left-rail>

<div class="endor-Page-content endor-Panel">
    <action-bar
        selected-components="selectedComponents"
        toggleable-columns="toggleableColumns"
        refresh-component-list="refreshComponentList()">
    </action-bar>
    <filter-pills></filter-pills>
    <div class="js-endor-content endor-Panel-content endor-Panel-content--actionBarHeight">
        <component-table
            components="components"
            selected-components="selectedComponents"
            toggleable-columns="toggleableColumns">
        </component-table>
    </div>
    <spinner id="cmSpinner" large="true" center="true"></spinner>
    <modal></modal>
</div>

Within this structure, there is a directive called <spinner>. This directive displays a spinner graphic while data is being loaded and interacts with an Angular service named spinnerApi. By registering the spinner with the spinner API, other services can inject the spinner API and utilize methods like show and hide, passing in an ID to control the visibility of specific spinners.

In the mainCtrl controller, there is a function responsible for initiating data loading as soon as the controller is activated.

//spinnerApi.show('spinner1');
var data = Segment.query({
    /*...truncated for brevity...*/
}, function () {
    $scope.components = data;
    spinnerApi.hide('spinner1');
});

The initial call to spinnerApi.show is currently commented out. This is done because the spinner directive has not been fully processed at that point, and the spinner has not been registered with the API. Uncommenting this line at this stage would result in an exception since the spinner named 'spinner1' is not yet available. However, once the query callback is executed, the spinner becomes operational, allowing the call to succeed without issues.

To avoid this race condition and ensure that the spinner directive is processed and registered with the API before data loading begins, how can this be achieved?

javascript angularjs controller angularjs-directive angularjs-scope

Answer 1

Answer №1

Consider a different approach:

Implement a method in your controller to set a flag on the scope indicating if the API is loading. Pass this flag to the directive within the template and utilize it in the directive's link function to toggle the spinner. It is recommended to use the prelink function over the postlink function for better performance when working with element display (DOM rendering optimization). Set the spinner visibility during prelink execution outside of the watcher to avoid waiting for the first digest loop to hide the spinner which has already been displayed once!

If multiple behaviors can affect the display flag, create a service to manage this flag. Share this service on the controller's scope and pass the flag as an input to the directive in the template. Avoid injecting this service directly into the directive to prevent excessive coupling between the spinner directive and its visibility condition.

Edit from question author:

This solution inspired me to develop a minimal and effective idea. I wanted to centralize any logic related to waiting in the 'spinnerApi' service instead of cluttering the controller or directive with such tasks (for reusability across the application).

Below is the updated 'spinnerApi' service, enhanced to queue hide/show/toggle events until the spinnerId registration occurs. The 'register' method now checks the queue for pending actions when invoked.

module.exports = angular.module('shared.services.spinner-api', [])
    // Simple API for easy spinner control.
    .factory('spinnerApi', function () {
        var spinnerCache = {};
        var queue = {};
        return {
            // All spinners are stored here.
            // Ex: { spinnerId: isolateScope }
            spinnerCache: spinnerCache,

            // Registers a spinner with the spinner API.
            // This method is only ever really used by the directive itself, but
            // the API could be used elsewhere if necessary.
            register: function (spinnerId, spinnerData) {

                // Add the spinner to the collection.
                this.spinnerCache[spinnerId] = spinnerData;

                // Increase the spinner count.
                this.count++;

                // Check if spinnerId was in the queue, if so then fire the
                // queued function.
                if (queue[spinnerId]) {
                    this[queue[spinnerId]](spinnerId);
                    delete queue[spinnerId];
                }

            },

            // Removes a spinner from the collection.
            unregister: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) throw new Error('Spinner "' + spinnerId + '" does not exist.');
                delete this.spinnerCache[spinnerId];
            },

            // Show a spinner with the specified spinnerId.
            show: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) {
                    queue[spinnerId] = 'show';
                    return;
                }
                this.spinnerCache[spinnerId].visible = true;
            },

            // Hide a spinner with the specified spinnerId.
            hide: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) {
                    queue[spinnerId] = 'hide';
                    return;
                }
                this.spinnerCache[spinnerId].visible = false;
            },

            // Hide/show a spinner with the specified spinnerId.
            toggle: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) {
                    queue[spinnerId] = 'toggle';
                    return;
                }
                this.spinnerCache[spinnerId].visible = !this.spinnerCache[spinnerId].visible;
            },

            // Show all spinners tracked by the API.
            showAll: function () {
                for (var key in this.spinnerCache) {
                    this.show(key);
                }
            },

            // Hide all spinners tracked by the API.
            hideAll: function () {
                for (var key in this.spinnerCache) {
                    this.hide(key);
                }
            },

            // Hide/show all spinners tracked by the API.
            toggleAll: function () {
                for (var key in this.spinnerCache)
                    this.spinnerCache[key].visible = !this.spinnerCache[key].visible;
            },

            // The number of spinners currently tracked by the API.
            count: 0
        };
    });

Answer 2

Consider a different approach:

Implement a method in your controller to set a flag on the scope indicating if the API is loading. Pass this flag to the directive within the template and utilize it in the directive's link function to toggle the spinner. It is recommended to use the prelink function over the postlink function for better performance when working with element display (DOM rendering optimization). Set the spinner visibility during prelink execution outside of the watcher to avoid waiting for the first digest loop to hide the spinner which has already been displayed once!

If multiple behaviors can affect the display flag, create a service to manage this flag. Share this service on the controller's scope and pass the flag as an input to the directive in the template. Avoid injecting this service directly into the directive to prevent excessive coupling between the spinner directive and its visibility condition.

Edit from question author:

This solution inspired me to develop a minimal and effective idea. I wanted to centralize any logic related to waiting in the 'spinnerApi' service instead of cluttering the controller or directive with such tasks (for reusability across the application).

Below is the updated 'spinnerApi' service, enhanced to queue hide/show/toggle events until the spinnerId registration occurs. The 'register' method now checks the queue for pending actions when invoked.

module.exports = angular.module('shared.services.spinner-api', [])
    // Simple API for easy spinner control.
    .factory('spinnerApi', function () {
        var spinnerCache = {};
        var queue = {};
        return {
            // All spinners are stored here.
            // Ex: { spinnerId: isolateScope }
            spinnerCache: spinnerCache,

            // Registers a spinner with the spinner API.
            // This method is only ever really used by the directive itself, but
            // the API could be used elsewhere if necessary.
            register: function (spinnerId, spinnerData) {

                // Add the spinner to the collection.
                this.spinnerCache[spinnerId] = spinnerData;

                // Increase the spinner count.
                this.count++;

                // Check if spinnerId was in the queue, if so then fire the
                // queued function.
                if (queue[spinnerId]) {
                    this[queue[spinnerId]](spinnerId);
                    delete queue[spinnerId];
                }

            },

            // Removes a spinner from the collection.
            unregister: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) throw new Error('Spinner "' + spinnerId + '" does not exist.');
                delete this.spinnerCache[spinnerId];
            },

            // Show a spinner with the specified spinnerId.
            show: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) {
                    queue[spinnerId] = 'show';
                    return;
                }
                this.spinnerCache[spinnerId].visible = true;
            },

            // Hide a spinner with the specified spinnerId.
            hide: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) {
                    queue[spinnerId] = 'hide';
                    return;
                }
                this.spinnerCache[spinnerId].visible = false;
            },

            // Hide/show a spinner with the specified spinnerId.
            toggle: function (spinnerId) {
                if (!this.spinnerCache[spinnerId]) {
                    queue[spinnerId] = 'toggle';
                    return;
                }
                this.spinnerCache[spinnerId].visible = !this.spinnerCache[spinnerId].visible;
            },

            // Show all spinners tracked by the API.
            showAll: function () {
                for (var key in this.spinnerCache) {
                    this.show(key);
                }
            },

            // Hide all spinners tracked by the API.
            hideAll: function () {
                for (var key in this.spinnerCache) {
                    this.hide(key);
                }
            },

            // Hide/show all spinners tracked by the API.
            toggleAll: function () {
                for (var key in this.spinnerCache)
                    this.spinnerCache[key].visible = !this.spinnerCache[key].visible;
            },

            // The number of spinners currently tracked by the API.
            count: 0
        };
    });

Answer 3

Answer №2

Compile is executed before the controller, which in turn runs before the link function. Therefore, any modifications or additions you are making in your link declaration should actually be done during the compile phase.

Given that you are utilizing a service to manage states shared between directives and controllers, you have the flexibility to add or remove spinners as needed, regardless of their sequence of execution. This means, based on your code snippet, instead of registering a spinner, you can simply toggle its state when reaching the link function in your directive:


module.exports = angular.module('shared.directives.spinner', [
  require('services/spinner-api').name
]).directive('spinner', function (spinnerApi){
  return {
    restrict: 'AE',
    template: '<div ng-show="visible" class="coral-Wait" ng-class="{ \'coral-Wait--center\': center, \'coral-Wait--large\': large }"></div>',
    replace : true,
    scope   : {},
    priority: 100,
    compile : function (){
      return {
        pre: function (scope, element, attrs, controller){
          // Obtain the spinner ID, either specified manually or default to spinnerApi count.
          var spinnerId = typeof(attrs.id) !== 'undefined' ? attrs.id : spinnerApi.count;
          // Set isolate scope variables.
          // scope.visible = !!attrs.visible || false;
          scope.center = !!attrs.center || false;
          scope.large = !!attrs.large || false;

          // Add the spinner to the spinner API.
          // The API maintains a simple object with spinnerId as key 
          // and the spinner's isolate scope as value.
          spinnerApi.register(spinnerId, scope);
        }
      };
    }
  };
});


app.factory('spinnerApi', function(){
   var spinnerApi;
   spinnerApi.repo = {};
   spinnerApi.show = function(name){
     if (!spinnerApi.repo[name]) {
       spinnerApi.repo[name] = {show: false}; 
     }
     spinnerApi.repo[name].show = true;
   } 
   spinnerApi.register = function(id, scope){ 
     if (!spinnerApi.repo[name]){
       spinnerApi.repo[name] = {show: false};
     }
     spinnerApi.repo[name].scope = scope;
     scope.$watch(function(){
       return spinnerApi.repo[name].show;
     }, function(newval, oldval){
        if (newval){
          spinnerApi.repo[name].scope.visible = newval;
        }
     });
   };
   /* "pseudo" code */
   return spinnerApi;
});

In my opinion, services should not directly interact with scopes. Services should hold the "raw state", leaving it to directives to handle actions based on that state. Consequently, the $watch logic should ideally be integrated within the isolated scope of your directive.

Answer 4

Compile is executed before the controller, which in turn runs before the link function. Therefore, any modifications or additions you are making in your link declaration should actually be done during the compile phase.

Given that you are utilizing a service to manage states shared between directives and controllers, you have the flexibility to add or remove spinners as needed, regardless of their sequence of execution. This means, based on your code snippet, instead of registering a spinner, you can simply toggle its state when reaching the link function in your directive:


module.exports = angular.module('shared.directives.spinner', [
  require('services/spinner-api').name
]).directive('spinner', function (spinnerApi){
  return {
    restrict: 'AE',
    template: '<div ng-show="visible" class="coral-Wait" ng-class="{ \'coral-Wait--center\': center, \'coral-Wait--large\': large }"></div>',
    replace : true,
    scope   : {},
    priority: 100,
    compile : function (){
      return {
        pre: function (scope, element, attrs, controller){
          // Obtain the spinner ID, either specified manually or default to spinnerApi count.
          var spinnerId = typeof(attrs.id) !== 'undefined' ? attrs.id : spinnerApi.count;
          // Set isolate scope variables.
          // scope.visible = !!attrs.visible || false;
          scope.center = !!attrs.center || false;
          scope.large = !!attrs.large || false;

          // Add the spinner to the spinner API.
          // The API maintains a simple object with spinnerId as key 
          // and the spinner's isolate scope as value.
          spinnerApi.register(spinnerId, scope);
        }
      };
    }
  };
});


app.factory('spinnerApi', function(){
   var spinnerApi;
   spinnerApi.repo = {};
   spinnerApi.show = function(name){
     if (!spinnerApi.repo[name]) {
       spinnerApi.repo[name] = {show: false}; 
     }
     spinnerApi.repo[name].show = true;
   } 
   spinnerApi.register = function(id, scope){ 
     if (!spinnerApi.repo[name]){
       spinnerApi.repo[name] = {show: false};
     }
     spinnerApi.repo[name].scope = scope;
     scope.$watch(function(){
       return spinnerApi.repo[name].show;
     }, function(newval, oldval){
        if (newval){
          spinnerApi.repo[name].scope.visible = newval;
        }
     });
   };
   /* "pseudo" code */
   return spinnerApi;
});

In my opinion, services should not directly interact with scopes. Services should hold the "raw state", leaving it to directives to handle actions based on that state. Consequently, the $watch logic should ideally be integrated within the isolated scope of your directive.

What steps can I take to guarantee that a directive's link function is executed prior to a controller?

Answer №1

Edit from question author:

Answer №2

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