One of the most powerful features in Angular is the ability to create custom directives. They allow you to write more modularized code that can be re-used throughout your application. However, understanding how scope works within a custom directive can often be confusing and is by no means obvious. How does your directive access scope properties on a controller? How do you give a directive it’s own scope? How can you isolate your directive’s scope from the rest of your application? We will address these questions and more in this post.

Overview

I have found that there are 4 primary ways to configure a directive’s scope, each of which can be useful in different scenarios. I am sure there are hybrids of these 4 configurations, but these will at least give you a solid foundation to start from. It is often helpful to give things memorable names when learning, so I will refer to these scope configurations as follows (each will be explained in more detail later):

  1. Moocher

    The directive does not have any scope of its own and just uses (mooches) the scope of the view that contains it. Everything in the controller’s scope is accessible from the directive.

  2. Borrower

    The directive has a scope of it’s own and it also inherits (borrows) the scope of the view that contains it. Everything in the controller’s scope is accessible from the directive.

  3. Loner

    The directive has its own isolated (loner) scope. The directive’s scope does not inherit anything from the scope of the view that contains it. It is a lone ranger.

  4. Negotiator

    The directive has it’s own scope and shares (negotiates) the scope of the view that contains it. One-way and two-way data binding of scope properties can be configured, as well as function/expression bindings. Only the scope properties configured to be “shared” are accessible from the directive.

NOTE: The examples below are using the angular “controller as” syntax (learn about it here). If you don’t know what that is just know that the controller scope on the views is referred to as vm, as in vm.scopePropertyName.

Moocher

Controller

The PersonCtrl controller sets three properties on the person object defined on it’s scope: firstName, lastName, and speak.

angular.module("app")
    .controller("PersonCtrl", function () {
        var vm = this;
        vm.person = {
            firstName: "Cosmo",
            lastName: "Kramer",
            speak: function () {
                return `Hello, my name is ${vm.person.firstName} ${vm.person.lastName}.`;
            }
        };
    });

Directive

The moocher directive has no scope of it’s own and will use the scope of the view that contains it (PersonCtrl in our example). This scope is the scope parameter passed to the link() function on the directive. You don’t have to do anything with this scope if you don’t want (you don’t even need to define a link() function at all). However, if you want to add data or behaviors to the scope from the directive, you can do something like what we are doing with msgFromDirective. The controller and all instances of the directive will share the same scope and their data will be in sync.

angular.module("app")
    .directive("moocher", function () {
       return {
           templateUrl: "examples/moocher/moocher.html",
           // optional: add properties to the scope
           link: function (scope, element, attrs) { 
               scope.vm.msgFromDirective = "Message from the 'person' directive!"
           }
       };
    });

Main View

All the properties put on the scope by the PersonCtrl controller and all the properties added to the scope in the link() function of the directive will be available to the main view.

<h3>Controller</h3>
<div class="well well-sm">
    <div class="form-inline">
        <div class="form-group">
            <label for="firstName">First Name</label>
            <input type="text" name="firstName" id="firstName" ng-model="vm.person.firstName" />
        </div>
        <div class="form-group">
            <label for="lastName">Last Name</label>
            <input type="text" name="lastName" id="lastName" ng-model="vm.person.lastName" />
        </div>
    </div>

    <div>First Name: {{vm.person.firstName}}</div>
    <div>Last Name: {{vm.person.lastName}}</div>
    <div>{{vm.person.speak()}}</div>
    <div>{{vm.msgFromDirective}}</div>
</div>


<h3>Moocher #1</h3>
<div class="well well-sm">
    <moocher></moocher>
</div>

Moocher View

(same story as the main view above)

<div>First Name: {{vm.person.firstName}}</div>
<div>Last Name: {{vm.person.lastName}}</div>
<div>{{vm.person.speak()}}</div>
<div>{{vm.msgFromDirective}}</div>

Borrower

Controller

The CarCtrl controller sets three properties on the car object defined in it’s scope: make, model, and getInfo.

angular.module("app")
    .controller("CarCtrl", function () {
        var vm = this;
        vm.car = {
            make: "Ford",
            model: "Focus",
            getInfo: function () {
                return `I am a ${vm.car.model} made by ${vm.car.make}.`;
            }
        }
    });

Directive

The borrower directive has a scope of its own provided by BorrowerCtrl and also inherits from the scope of the view that contains it (CarCtrl is our example). This is accomplished by the scope on the directive being set to true. The BorrowerCtrl adds a year property to the car object on it’s scope.

angular.module("app")
    .directive("borrower", function () {
        return {
            templateUrl: "examples/borrower/borrower.html",
            scope: true
        };
    })
    .controller("BorrowerCtrl", function () {
        this.car = {
            year: 2016
        };
    });

Main View

The main view can access it’s scope properties as usual, but cannot access the year property that the borrower directive added to it’s own scope. The {{vm.year}} will display nothing.

<h3>From Controller</h3>

<div class="well well-sm">
    <div class="form-inline">
        <div class="form-group">
            <label for="make">Make</label>
            <input type="text" name="make" id="make" ng-model="vm.car.make" />
        </div>
        <div class="form-group">
            <label for="model">Model</label>
            <input type="text" name="model" id="model" ng-model="vm.car.model" />
        </div>
    </div>

    <div>Make: {{vm.car.make}}</div>
    <div>Model: {{vm.car.model}}</div>
    <div>{{vm.car.getInfo()}}</div>
    <div>Year: {{vm.year}}</div> <!-- cannot access the directives scope -->
</div>


<h3>Borrower #1</h3>
<div class="well well-sm">
    <borrower></borrower>
</div>

<h3>Borrower #2</h3>
<div class="well well-sm">
    <borrower></borrower>
</div>

Borrower View

The view for the borrower directive is able to access the CarCtrl’s scope properties via vm. The BorrowerCtrl scope to borrowerVm, which allows us to display the year property via {{borrowerVm.car.year}}. Every instance of borrower will inherit the same scope from CarCtrl, but will get it’s own scope from BorrowerCtrl. This mean that updates to make & model will effect the main view and all directive views, but changes to year will only effect that BorrowerCtrl’s scope & view.

<div ng-controller="BorrowerCtrl as borrowerVm">
    <div class="form-inline">
        <div class="form-group">
            <label for="year">Year</label>
            <input type="text" name="year" id="year" ng-model="borrowerVm.car.year" />
        </div>
    </div>
    
    <div>Make: {{vm.car.make}}</div>
    <div>Model: {{vm.car.model}}</div>
    <div>{{vm.car.getInfo()}}</div>
    <div>Year: {{borrowerVm.car.year}}</div>
</div>

Loner

This StereoCtrl controller sets three properties on the stereo object defined in it’s scope: min, max, and getInfo.

Controller

angular.module("app")
    .controller("StereoCtrl", function () {
        var vm = this;
        vm.stereo = {
            min: 0,
            max: 10,
            getInfo: function () {
                return `This stereo goes from ${vm.stereo.min} to ${vm.stereo.max}`;
            }
        }
    });

Directive

The loner directive does not inherit any scope, but has it’s own totally isolated scope provided by the LonerCtrl. This is accomplished by the scope on the directive being set to {}. The LonerCtrl defines it’s own min & max scope properties on it’s own stereo object, which will override the one on StereoCtrl.

angular.module("app")
    .directive("loner", function () {
        return {
            templateUrl: "examples/loner/loner.html",
            scope: {}
        }
    })
    .controller("LonerCtrl", function () {
        this.stereo = {
            min: 5,
            max: 11
        }
    });

Main View

Nothing special here, just basic model binding that we have already seen.

<h3>From Controller</h3>

<div class="well well-sm">
    <div class="form-inline">
        <div class="form-group">
            <label for="min">Min</label>
            <input type="text" name="min" id="min" ng-model="vm.stereo.min" />
        </div>
        <div class="form-group">
            <label for="max">Max</label>
            <input type="text" name="max" id="max" ng-model="vm.stereo.max" />
        </div>
    </div>
    
    <div>Min: {{vm.stereo.min}}</div>
    <div>Max: {{vm.stereo.max}}</div>
    <div>Info: {{vm.stereo.getInfo()}}</div>
</div>


<h3>Loner #1</h3>
<div class="well well-sm">
    <loner></loner>
</div>

<h3>Loner #2</h3>
<div class="well well-sm">
    <loner></loner>
</div>

Loner View

The loner directive view will use the scope provided by the LonerCtrl. It defines it’s own stereo object with min & max scope properties with different values than the ones on StereoCtrl. Each instance of the loner directive will get its own isolated version of the LonerCtrl. This means that if you change the min or max on a directive it will not effect any of the other instances of the directive.

<div ng-controller="LonerCtrl as vm">
    <div class="form-inline">
        <div class="form-group">
            <label for="min">Min</label>
            <input type="text" name="min" id="min" ng-model="vm.stereo.min" />
        </div>
        <div class="form-group">
            <label for="max">Max</label>
            <input type="text" name="max" id="max" ng-model="vm.stereo.max" />
        </div>
    </div>
    
    <div>Min: {{vm.stereo.min}}</div>
    <div>Max: {{vm.stereo.max}}</div>
    <div>Info: {{vm.stereo.getInfo()}}</div>
</div>

Negotiator

Controller

The IceCreamCtrl controller sets three properties on the iceCream object in it’s scope: min, max, and getInfo. An alertText function property is also set on the scope that will simply alert whatever text it receives in it’s parameter.

angular.module("app")
    .controller("IceCreamCtrl", function () {
        var vm = this;
        vm.iceCream = {
            flavor: "Vanilla",
            size: "Medium",
            getInfo: function () {
                return `I have a ${vm.iceCream.size} ${vm.iceCream.flavor} ice cream.`
            }
        };
        vm.alertText = function (text) {
            alert(text);
        }
    });

Directive

This is where things get fun! The negotiator directive has it’s own scope, but negotiates with the scope of the view that contains it (IceCreamCtrl in our example). A scope property named flavaFlave will be created and have a one-way binding with the property flavor that is passed to the instance of the directive (will make more sense when looking at the main view below). A scope property named howBig will be created and have a two-way binding with the property size that is passed to the instance of the directive. A scope function property named getTheDeets will be created and assigned to the property getInfo that is passed to the instance of the directive. Lastly, a scope function named soundTheAlarm will be created and assigned to the property alertText that is passed to the instance of the directive. The function will be passed isolated scope data from the directive’s isolated scope (more on that later). Here is a simple way to remember the binding syntax:

  • @ = one-way
  • = = two-way
  • & = function/expression binding
angular.module("app")
    .directive("negotiator", function () {
        return {
            templateUrl: "examples/negotiator/negotiator.html",
            link: function (scope) {
                // can add private members to the isolated scope here
                scope.message = "This is my message.";
            },
            scope: {
                // one way
                flavaFlave: "@flavor",
                // two way
                howBig: "=size", 
                // expression (function)
                getTheDeets: "&getInfo",
                // expression that takes isolated scope data
                soundTheAlarm: "&alertText"
            }
        }
    });

Main View

The only new stuff going on in this view is the <negotiator> elements at the bottom. Notice how we are setting attributes on the <negotiator> element that correspond to the scope bindings mentioned above in the directive section. That is how the negotiator directive binds it’s scope properties.

One important thing to see is the vm.alert(blah) we are setting to the alert-text attribute. What is that blah all about? It is the name of the property we are going to use in our call to getInfo from the directive’s view. This will allow us to take data from our directive’s isolated scope and use it as the parameter to the getInfo function on the controller’s scope.

<h3>From Controller</h3>

<div class="well well-sm">
    <div class="form-inline">
        <div class="form-group">
            <label for="flavor">Flavor</label>
            <input type="text" name="flavor" id="flavor" ng-model="vm.iceCream.flavor" />
        </div>
        <div class="form-group">
            <label for="size">Size</label>
            <input type="text" name="size" id="size" ng-model="vm.iceCream.size" />
        </div>
    </div>
    
    <div>Flavor: {{vm.iceCream.flavor}}</div>
    <div>Size: {{vm.iceCream.size}}</div>
    <div>Info: {{vm.iceCream.getInfo()}}</div>
</div>


<h3>Negotiator #1</h3>
<negotiator 
    flavor="{{vm.iceCream.flavor}}"
    size="vm.iceCream.size"
    get-info="vm.iceCream.getInfo()"
    alert-text="vm.alertText(blah)">
</negotiator>

<h3>Negotiator #2</h3>
<negotiator 
    flavor="{{vm.iceCream.flavor}}"
    size="vm.iceCream.size"
    get-info="vm.iceCream.getInfo()"
    alert-text="vm.alertText(blah)">
</negotiator>

Negotiator View

Most of what we see in this view is stuff we have seen before; binding to properties on the directive’s scope. The one thing to point out is the ng-click="soundTheAlarm({blah: message})". As we mentioned above, blah is the name of property we are using to allow us to pass in data from our directive’s isolated scope as the parameter to the alertText method on the controller’s scope.

<div class="well well-sm">
    <div class="form-inline">
        <div class="form-group">
            <label for="flavaFlave">Flava Flave</label>
            <input type="text" name="flavaFlave" id="flavaFlave" ng-model="flavaFlave" />
        </div>
        <div class="form-group">
            <label for="howBig">How Big</label>
            <input type="text" name="howBig" id="howBig" ng-model="howBig" />
        </div>
        <div class="form-group">
            <label for="message">Message</label>
            <input type="text" name="message" id="message" ng-model="message" />
        </div>
        <div class="form-group">
            <button class="btn btn-primary" ng-click="soundTheAlarm({blah: message})">
                Sound The Alarm
            </button>
        </div>
    </div>

    <div>Flava Flave: {{flavaFlave}}</div>
    <div>How Big: {{howBig}}</div>
    <div>Info: {{getTheDeets()}}</div>
</div>