The “with” binding of KnockoutJS in AngularJS?

问题:

I have just switched from KnockoutJS to AngularJS and I am not able to find the KnockoutJS's "with" data-bind in AngularJS.

Here is the piece of code in KnockoutJS. The "with" binding creates a new binding context, so that descendant elements are bound in the context of a specified object.

<h1 data-bind="text: city"> </h1>
<p data-bind="with: coords">
    Latitude: <span data-bind="text: latitude"> </span>,
    Longitude: <span data-bind="text: longitude"> </span>
</p>

<script type="text/javascript">
    ko.applyBindings({
        city: "London",
        coords: {
            latitude:  51.5001524,
            longitude: -0.1262362
        }
    });
</script>

Does AngularJS have anything like context?

回答1:

Nothing like with that I know of.. this is the best I could do:

<h1>{{city}}</h1>
<p ng-repeat="c in [coords.or.possibly.deeper.in.tree]">
    Latitude: {{c.latitude}},
    Longitude: {{c.longitude}}
</p>

回答2:

Create a custom directive that loops through the source object and creates corresponding properties on the directive's scope that are getter/setter references to the source object.

Check out this plunker.

directive module:

angular.module('koWith', [])
  .directive('koWith', function () {
    return {
      controller: function ($scope, $attrs) {
        var withObj = $scope.$parent[$attrs.ngWith];

        function getter(prop) {
          return this[prop];
        }
        function setter(val, prop) {
          this[prop] = val;
        }

        for (var prop in withObj) {
          if (withObj.hasOwnProperty(prop)) {
            Object.defineProperty($scope, prop, {
              enumerable: true,
              configurable: true,
              get: getter.bind(withObj, prop),
              set: setter.bind(withObj, prop)
            });
          }
        }
      },
      restrict: 'A',
      scope: true
    };
  });

app module:

angular.module('myApp', [])
  .controller('myController', function ($scope) {
    $scope.customer = {
      name: "Timmeh",
      address: {
        address1: "12 S Street",
        address2: "",
        city: "South Park",
        state: "CO",
        zipCode: "80440"
      }
    };
  });

html:

<div ko-with="customer">
  <h2>{{name}}</h2>
  <div ko-with="address">
    {{address1}}<br>
    {{address2}}<br>
    {{city}}, {{state}} {{zipCode}}
  </div>
</div>

Explanation

In KnockoutJS, bindings keep the bindingContext and data separated so creating the with binding is trivial since it only needs to create a new child bindingContext from the current one and use the with object as its data value.

In AngularJS, a directive's scope is basically the bindingContext and data object rolled into one. When a new scope is created, in order to get the with-like behavior, the properties of the with object have to be referenced onto the newly created scope object.

回答3:

Here is solution based on @nwayve, but it supports expressions in koWith and also it watches for updating property/expression specified in koWith:

.directive('koWith', function () {
return {
    restrict: 'A',
    scope: true,
    controller: function ($scope, $attrs, $parse) {
        var ScopePropertyDesc = function (prop) {
            var self = this;
            self.propName = prop;
            self.parsed = $parse(prop);
            self.enumerable = true;
            self.configurable = true;
            //self.writable = true;
            self.get = function () {
                var withObj = $scope.$parent[$attrs.koWith];
                var res = self.parsed($scope.$parent, withObj);
                return res;
            };
            self.set = function (newValue) {
                var withObj = $scope.$parent[$attrs.koWith];
                self.parsed.assign(withObj, newValue);
            };
        };

        $scope.$parent.$watch($attrs.koWith, function (oldVal, newVal) {
            var withObj = $scope.$parent[$attrs.koWith];

            (function copyPropertiesToScope(withObj) {
                for (var prop in withObj) {
                    if (withObj.hasOwnProperty(prop)) {
                        Object.defineProperty($scope, prop, new ScopePropertyDesc(prop));
                    }
                };
            })(withObj);
        });
    }
};
});