Accessing attributes from an AngularJS directive

Question

My AngularJS template contains some custom HTML syntax like:

<su-label tooltip="{{field.su_documentation}}">{{field.su_name}}</su-label>

I created a directive to process it:

.directive('suLabel', function() {
  return {
    restrict: 'E',
    replace: true,
    transclude: true,
    scope: {
      title: '@tooltip'
    },
    template: '<label><a href="#" rel="tooltip" title="{{title}}" data-placement="right" ng-transclude></a></label>',
    link: function(scope, element, attrs) {
      if (attrs.tooltip) {
        element.addClass('tooltip-title');
      }
    },
  }
})

Everything works fine, at the exception of the attrs.tooltip expression, which always returns undefined, even though the tooltip attribute is visible from Google Chrome's JavaScript console when doing a console.log(attrs).

Any suggestion?

UPDATE: A solution was offered by Artem. It consisted in doing this:

link: function(scope, element, attrs) {
  attrs.$observe('tooltip', function(value) {
    if (value) {
      element.addClass('tooltip-title');
    }
  });
}

AngularJS + stackoverflow = bliss

This [answer](http://stackoverflow.com/questions/12008580/a-ternary-in-angular-templates-angularjs/12151492#12151492) to another question explains how to properly express a ternary in AngularJS. — Ismael Ghalimi, Aug 28 '12 at 04:08

Artem Andreev · Accepted Answer · 2015-01-08T08:48:40.970

83

See section Attributes from documentation on directives.

observing interpolated attributes: Use $observe to observe the value changes of attributes that contain interpolation (e.g. src="{{bar}}"). Not only is this very efficient but it's also the only way to easily get the actual value because during the linking phase the interpolation hasn't been evaluated yet and so the value is at this time set to undefined.

edited Jan 08 '15 at 08:48

answered Aug 11 '12 at 10:31

Artem Andreev

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URL is now changed to http://docs.angularjs.org/api/ng/service/$compile#Attributes – bhatiaravi Mar 25 '14 at 12:49

score 25 · Answer 2 · answered Jan 03 '13 at 16:47

Although using '@' is more appropriate than using '=' for your particular scenario, sometimes I use '=' so that I don't have to remember to use attrs.$observe():

<su-label tooltip="field.su_documentation">{{field.su_name}}</su-label>

Directive:

myApp.directive('suLabel', function() {
    return {
        restrict: 'E',
        replace: true,
        transclude: true,
        scope: {
            title: '=tooltip'
        },
        template: '<label><a href="#" rel="tooltip" title="{{title}}" data-placement="right" ng-transclude></a></label>',
        link: function(scope, element, attrs) {
            if (scope.title) {
                element.addClass('tooltip-title');
            }
        },
    }
});

Fiddle.

With '=' we get two-way databinding, so care must be taken to ensure scope.title is not accidentally modified in the directive. The advantage is that during the linking phase, the local scope property (scope.title) is defined.

Hey Mark, what is your opinion on using these solutions, is there a specific guideline for using observe on the link attrs against using the two-way-databinding ? I think it looks cleaner to use the two-way databinding but I wonder if there is a reason to not use it? — Jeroen, Jan 06 '15 at 12:15
@Jeroen, I posted a longer discussion of using `@` vs `=` [here](http://stackoverflow.com/a/14063373/215945). — Mark Rajcok, Jan 07 '15 at 17:11

Accessing attributes from an AngularJS directive

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