Change Angular directive element attribute dynamically

Question

I am trying to create a custom directive which extends the functionality of an existing element. I would like to detect if a certain attribute exists and if not then add it (e.g. ng-class).

I have tried to achieve this during pre-compilation but angular does not react to the addition of the new attribute.

I created a plunker with a simple example using ng-hide.

<input hide type="submit" value="Submit"/>

    app.directive('hide', function() {
      return {
        restrict: 'A',
        compile: function(){
             return {
                 pre: function(scope, element, attributes, controller, transcludeFn){
                   attributes.$set("ng-hide", true);
                 },
                 post: function(scope, element, attributes, controller, transcludeFn){

                 }
             }
         },
      };
    });

If I add ng-hide="true" in the html then the submit button is hidden correctly. If I leave it to the directive then I can see that the DOM has the element set up correctly but the element is not hidden:

<input hide="" type="submit" value="Submit" ng-hide="true">

Any help appreciated!

Solution

You can do this in the linking function by

• Setting the directive's priority high, so it runs before all others.
• Set it to terminal, so others don't run after it.
• Recompile the element after you make changes to it (such as adding attributes)

For example:

app.directive('hide', function($compile) {
  return {
    restrict: 'A',
    priority: 10000,
    terminal: true,
    link: function(scope, element, attrs) {
      attrs.$set('ngHide', true);
      attrs.$set('hide', null);
      $compile(element)(scope);
   }
  };
});

As can be seen on http://plnkr.co/edit/tHNvCxVn2wURO38UtI0n?p=preview

Comments

[Alan]

You are a genius, thanks! I didn't need to set terminal in the end; priority and compiling the element (with the directive null) did the trick

[Michal Charemza]

I would keep the terminal: true. It might not be technically necessary in the current case, but it does prevent needless recompiling of any other directives on the element.