Use of symbols '@', '&', '=' and '>' in custom directive's scope binding: AngularJS

Question

I have read a lot about the use of these symbols in the implementation of custom directives in AngularJS but the concept is still not clear to me.

What does it mean if I

Answer 1

In an AngularJS directive the scope allows you to access the data in the attributes of the element to which the directive is applied.

This is illustrated best with an example:

and the directive definition:

angular.module('myModule', [])
.directive('myCustomer', function() {
  return {
    restrict: 'E',
    scope: {
      customerName: '@name'
    },
    controllerAs: 'vm',
    bindToController: true,
    controller: ['$http', function($http) {
      var vm = this;

      vm.doStuff = function(pane) {
        console.log(vm.customerName);
      };
    }],
    link: function(scope, element, attrs) {
      console.log(scope.customerName);
    }
  };
});

When the scope property is used the directive is in the so called "isolated scope" mode, meaning it can not directly access the scope of the parent controller.

In very simple terms, the meaning of the binding symbols is:

someObject: '=' (two-way data binding)

someString: '@' (passed directly or through interpolation with double curly braces notation {{}})

someExpression: '&' (e.g. hideDialog())

This information is present in the AngularJS directive documentation page, although somewhat spread throughout the page.

The symbol > is not part of the syntax.

However, < does exist as part of the AngularJS component bindings and means one way binding.