Is there a better solution than using a hacky Timeout for waiting on the DOM to be ready in a directive's link function?

Question

Is there a better solution than using a hacky Timeout for waiting on the DOM to be ready in a directive's link function?

Inside one of my custom directives, I have an ng-repeat in the template.

myApp.directive("test", function () {
    return {
   restrict: 'C',
     scope: {
      bindVar: '='
    },
        template: '<div>\
<div class="item" ng-repeat="sel in bindVar">{{sel.display}}</div>\
     </div>',
     link: function ($scope, element, attrs) {


     //   setTimeout(function() { 
        alert($('.item').length); // <--- RETURNS 0, IF I ADD TIMEOUT RETURNS 3
   // },0);



     } // of link
    } // of return
});

Check out this JSFiddle for reference

Despite calling the link() function, I'm unable to access the newly created items directly. A workaround involves setting a timeout of 0 milliseconds (after that it works).

I came across a blog post discussing this issue in detail: Handling DOM Updates in AngularJS

Additionally, there's a related Stack Overflow thread where using Timeout was marked as the solution: DOM elements not ready in AngularJS Directive's link() function

Hopefully, there's a more elegant approach than relying on timeouts. Is there a built-in method in Angular to trigger a callback when the DOM is fully generated by a directive? Or are timeouts the only way to go? (really? :/)

javascript angularjs angularjs-directive

Answer 1

Answer №1

$timeout is a valid solution when using inline template instead of templateUrl, and it does not lead to any race conditions.

Angular traverses the DOM, gathers directives along with their pre- and post-link functions by compiling them. Subsequently, the link functions for each directive on each node (i.e., DOM element) are executed.

In general, the template corresponding to the node (to which the directive applies) is already present in the DOM. Therefore, if you have the following directive:

.directive("foo", function(){
  return {
    template: '<span class="fooClass">foo</span>',
    link: function(scope, element){
      // Outputs "<span class="fooClass">foo</span>"
      console.log(element.html()); 
    }
  }
}

it can locate the $(".fooClass") element.

However, if a directive utilizes transclude: 'element', like ng-if and ng-repeat directives do, Angular converts the directive into a comment. As a result, $(".item") (as in your case) is not available until placed there by ng-repeat. This insertion occurs within their scope.$watch function, depending on the value being watched, potentially happening during the subsequent digest cycle. Hence, even after executing the post-link function, the actual sought-after element might still be absent.

.directive("foo", function(){
  return {
    template: '<span ng-if="true" class="fooClass">foo</span>',
    link: function(scope, element){
      // Outputs "<!-- ngIf: true -->"
      console.log(element.html());
    }
  }
}

Nevertheless, it will undoubtedly become available when $timeout is triggered.

Answer 2

$timeout is a valid solution when using inline template instead of templateUrl, and it does not lead to any race conditions.

Angular traverses the DOM, gathers directives along with their pre- and post-link functions by compiling them. Subsequently, the link functions for each directive on each node (i.e., DOM element) are executed.

In general, the template corresponding to the node (to which the directive applies) is already present in the DOM. Therefore, if you have the following directive:

.directive("foo", function(){
  return {
    template: '<span class="fooClass">foo</span>',
    link: function(scope, element){
      // Outputs "<span class="fooClass">foo</span>"
      console.log(element.html()); 
    }
  }
}

it can locate the $(".fooClass") element.

However, if a directive utilizes transclude: 'element', like ng-if and ng-repeat directives do, Angular converts the directive into a comment. As a result, $(".item") (as in your case) is not available until placed there by ng-repeat. This insertion occurs within their scope.$watch function, depending on the value being watched, potentially happening during the subsequent digest cycle. Hence, even after executing the post-link function, the actual sought-after element might still be absent.

.directive("foo", function(){
  return {
    template: '<span ng-if="true" class="fooClass">foo</span>',
    link: function(scope, element){
      // Outputs "<!-- ngIf: true -->"
      console.log(element.html());
    }
  }
}

Nevertheless, it will undoubtedly become available when $timeout is triggered.

Answer 3

Answer №2

A different approach I use involves implementing another directive. Here is an illustration:

.directive('elementReady', function() {
   return {
       restrict: 'A',
       link: function(scope, elem, attr) {
           //You can perform actions like:
           if(scope.$last) {
              //this element is the last one in an ng-repeat
           }
           if(scope.$first) {
              //first element in ng-repeat
           }

           //perform jQuery and JavaScript calculations (elem has been added to the DOM at this point)
       }
   };
});


<table class="box-table" width="100%">
        <thead>
            <tr>
                <th class='test' scope="col" ng-repeat="column in listcolumns" element-ready>{{column.title}}</th>
            </tr>
        </thead>
</table>

Of course, you will need to determine how to pass those events to your outer scope ($emit, using bound functions, etc).

Answer 4

A different approach I use involves implementing another directive. Here is an illustration:

.directive('elementReady', function() {
   return {
       restrict: 'A',
       link: function(scope, elem, attr) {
           //You can perform actions like:
           if(scope.$last) {
              //this element is the last one in an ng-repeat
           }
           if(scope.$first) {
              //first element in ng-repeat
           }

           //perform jQuery and JavaScript calculations (elem has been added to the DOM at this point)
       }
   };
});


<table class="box-table" width="100%">
        <thead>
            <tr>
                <th class='test' scope="col" ng-repeat="column in listcolumns" element-ready>{{column.title}}</th>
            </tr>
        </thead>
</table>

Of course, you will need to determine how to pass those events to your outer scope ($emit, using bound functions, etc).

Answer 5

Answer №3

By combining Joe's Answer with another helpful solution I discovered on stackoverflow, I was able to achieve the desired outcome:

myApp.directive('myRepeatDirective', function() {
  return function(scope, element, attrs) {
    if (scope.$last){
      scope.$emit('LastElem');
    }
  };
});

In my original link function, I included:

 $scope.$on('LastElem', function(event){
        alert($('.item').length);
    });

My template now looks like this:

<div>
<div class="item" ng-repeat="sel in bindVar" my-repeat-directive>{{sel.display}}</div>
</div>

http://jsfiddle.net/foreyez/t4590zbr/3/

Despite implementing this solution, I still have reservations about its effectiveness.. it just doesn't quite satisfy me.

Answer 6

By combining Joe's Answer with another helpful solution I discovered on stackoverflow, I was able to achieve the desired outcome:

myApp.directive('myRepeatDirective', function() {
  return function(scope, element, attrs) {
    if (scope.$last){
      scope.$emit('LastElem');
    }
  };
});

In my original link function, I included:

 $scope.$on('LastElem', function(event){
        alert($('.item').length);
    });

My template now looks like this:

<div>
<div class="item" ng-repeat="sel in bindVar" my-repeat-directive>{{sel.display}}</div>
</div>

http://jsfiddle.net/foreyez/t4590zbr/3/

Despite implementing this solution, I still have reservations about its effectiveness.. it just doesn't quite satisfy me.

Is there a better solution than using a hacky Timeout for waiting on the DOM to be ready in a directive's link function?

Answer №1

Answer №2

Answer №3

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