Exploring the Angular 1.5 .component() method

Angular 1.5 introduced the

.component()

helper method, which is much simpler than the

.directive()

definition and advocates best practices and common default behaviours. Using

.component()

will allow developers to write in an Angular 2 style as well, which will in turn make upgrading to Angular 2 an easier feat.

Let’s compare the differences in syntax and the super neat abstraction that

.component()

gives us over using the

.directive()

method.

Update: use component() now in Angular 1.3+

I’ve back-ported the Angular 1.5

.component()

functionality to Angular 1.3 and above! Read the article and grab the code on GitHub.

.directive() to .component()

The syntax change is very simple:

// before
module.directive(name, fn);

// after
module.component(name, options);

The

name

argument is what we want to define our Component as, the

options

argument is a definition Object passed into the component, rather than a function that we know so well in versions 1.4 and below.

I’ve prebuilt a simple

counter

component for the purposes of this exercise in Angular

1.4.x

which we’ll refactor into a version

v1.5.0

build to use

.component()

.

.directive('counter', function counter() {
return {
scope: {},
bindToController: {
count: '='
},
controller: function () {
function increment() {
this.count++;
}
function decrement() {
this.count--;
}
this.increment = increment;
this.decrement = decrement;
},
controllerAs: 'counter',
template: [
'<div class="todo">',
'<input type="text" ng-model="counter.count">',
'<button type="button" ng-click="counter.decrement();">-</button>',
'<button type="button" ng-click="counter.increment();">+</button>',
'</div>'
].join('')
};
});

A live embed of the

1.4.x

Directive:

We’ll continue building this alongside how we’d build the Angular 1.4 version to compare differences.

Function to Object, method name change

Let’s start from the top and refactor the

function

argument to become an

Object

, and change the name from

.directive()

to

.component()

:

// before
.directive('counter', function counter() {
return {

};
});

// after
.component('counter', {

});

Nice and simple. Essentially the

return {};

statement inside the

.directive()

becomes the Object definition inside

.component()

- easy!

“scope” and “bindToController”, to “bindings”

In a

.directive()

, the

scope

property allows us to define whether we want to isolate the

$scope

or inherit it, this has now become a sensible default to (usually) always make our Directives have isolate scope. So repeating ourselves each time just creates excess boilerplate. With the introduction of

bindToController

, we can explicitly define which properties we want to pass into our isolate scope and bind directly to the Controller.

With the

bindings

property on

.component()

we can remove this boilerplate and simply define what we want to pass down to the component, under the assumption that the component will have isolate scope.

// before
.directive('counter', function counter() {
return {
scope: {},
bindToController: {
count: '='
}
};
});

// after
.component('counter', {
bindings: {
count: '='
}
});

Controller and controllerAs changes

Nothing has changed in the way we declare

controller

, however it’s now a little smarter and has a default

controllerAs

value of

$ctrl

.

If we’re using a controller local to the component, we’ll do this:

// 1.4
{
...
controller: function () {}
...
}

If we’re using another Controller defined elsewhere, we’ll do this:

// 1.4
{
...
controller: 'SomeCtrl'
...
}

If we want to define

controllerAs

at this stage (which will over-ride the default

$ctrl

value), we’ll need to create a new property and define the instance alias:

// 1.4
{
...
controller: 'SomeCtrl',
controllerAs: 'something'
...
}

This then allows us to use

something.prop

inside our

template

to talk to the instance of the Controller.

Now, there are some changes in

.component()

that make sensible assumptions and automatically create a

controllerAs

property under the hood for us, and automatically assign a name based on three possibilities:

// inside angular.js
controllerAs: identifierForController(options.controller) || options.controllerAs || '$ctrl',

Possibility one uses this aptly named

identifierForController

function that looks like so:

// inside angular.js
var CNTRL_REG = /^(\S+)(\s+as\s+(\w+))?$/;
function identifierForController(controller, ident) {
if (ident && isString(ident)) return ident;
if (isString(controller)) {
var match = CNTRL_REG.exec(controller);
if (match) return match[3];
}
}

This allows us to do the following inside

.component()

:

// 1.5
{
...
controller: 'SomeCtrl as something'
...
}

This saves adding the

controllerAs

property… however…

We can add the

controllerAs

property to maintain backwards compatibility or keep it if that’s within your style for writing Directives/Components.

The third option, and better yet, completely removes all need to think about

controllerAs

, and Angular automatically uses the name

$ctrl

. For instance:

.component('test', {
controller: function () {
this.testing = 123;
}
});

The would-be

controllerAs

definition automatically defaults to

$ctrl

, so we can use

$ctrl.testing

in our

template

which would give us the value of

123

.

Based on this information, we add our

controller

, and refactor our Directive into a Component by dropping the

controllerAs

property:

// before
.directive('counter', function counter() {
return {
scope: {},
bindToController: {
count: '='
},
controller: function () {
function increment() {
this.count++;
}
function decrement() {
this.count--;
}
this.increment = increment;
this.decrement = decrement;
},
controllerAs: 'counter'
};
});

// after
.component('counter', {
bindings: {
count: '='
},
controller: function () {
function increment() {
this.count++;
}
function decrement() {
this.count--;
}
this.increment = increment;
this.decrement = decrement;
}
});

Things are becoming much simpler to use and define with this change.

Template

There’s a subtle difference in the

template

property worth noting. Let’s add the

template

property to finish off our rework and then take a look.

.component('counter', {
bindings: {
count: '='
},
controller: function () {
function increment() {
this.count++;
}
function decrement() {
this.count--;
}
this.increment = increment;
this.decrement = decrement;
},
template: [
'<div class="todo">',
'<input type="text" ng-model="$ctrl.count">',
'<button type="button" ng-click="$ctrl.decrement();">-</button>',
'<button type="button" ng-click="$ctrl.increment();">+</button>',
'</div>'
].join('')
});

The

template

property can be defined as a function that is now injected with

$element

and

$attrs

locals. If the

template

property is a function then it needs to return an String representing the HTML to compile:

{
...
template: function ($element, $attrs) {
// access to $element and $attrs
return [
'<div class="todo">',
'<input type="text" ng-model="$ctrl.count">',
'<button type="button" ng-click="$ctrl.decrement();">-</button>',
'<button type="button" ng-click="$ctrl.increment();">+</button>',
'</div>'
].join('')
}
...
}

That’s it for our Directive to Component refactor, however there are a few other changes worth exploring before we finish.

Inheriting behaviour using “require”

If you’re not familiar with “require”, check my article on using require.

{
...
require: {
parent: '^parentComponent'
},
controller: function () {
// use this.parent to access required Objects
this.parent.foo();
}
...
}

Inherited Directive or Component methods will be bound to the

this.parent

property in the Controller.

One-way bindings

A new syntax expression for isolate scope values, for example:

{
...
bindings: {
oneWay: '<',
twoWay: '='
},
...
}

Read my full write-up about one-way bindings.

Disabling isolate scope

Components are always created with isolate scope. Here’s the relevant part from the source code:

{
...
scope: {},
...
}

Stateless components

There’s now the ability to create “stateless” components, read my in-depth article onstateless components in the

.component()

method.

Essentially we can just use a

template

and

bindings

:

var NameComponent = {
bindings: {
name: '=',
age: '='
},
template: [
'<div>',
'<p>Name: </p>',
'<p>Age: </p>',
'</div>'
].join('')
};

angular
.module('app', [])
.component('nameComponent', NameComponent);

Sourcecode for comparison

Throughout the article I’ve referred to some Angular source code snippets to cross reference against. Here’s the source code below:

this.component = function registerComponent(name, options) {
var controller = options.controller || function() {};

function factory($injector) {
function makeInjectable(fn) {
if (isFunction(fn) || isArray(fn)) {
return function(tElement, tAttrs) {
return $injector.invoke(fn, this, {$element: tElement, $attrs: tAttrs});
};
} else {
return fn;
}
}

var template = (!options.template && !options.templateUrl ? '' : options.template);
return {
controller: controller,
controllerAs: identifierForController(options.controller) || options.controllerAs || '$ctrl',
template: makeInjectable(template),
templateUrl: makeInjectable(options.templateUrl),
transclude: options.transclude,
scope: {},
bindToController: options.bindings || {},
restrict: 'E',
require: options.require
};
}

// Copy any annotation properties (starting with $) over to the factory function
// These could be used by libraries such as the new component router
forEach(options, function(val, key) {
if (key.charAt(0) === '$') {
factory[key] = val;
}
});

factory.$inject = ['$injector'];

return this.directive(name, factory);
};

Again, please note that Angular 1.5 isn’t released just yet, so this article uses an API thatmay be subject to slight change.

Upgrading to Angular 2

Writing components in this style will allow you to upgrade your Components using

.component()

into Angular 2 very easily, it’d look something like this in ECMAScript 5 and new template syntax:

var Counter = ng
.Component({
selector: 'counter',
template: [
'<div class="todo">',
'<input type="text" [(ng-model)]="count">',
'<button type="button" (click)="decrement();">-</button>',
'<button type="button" (click)="increment();">+</button>',
'</div>'
].join('')
})
.Class({
constructor: function () {
this.count = 0;
},
increment: function () {
this.count++;
},
decrement: function () {
this.count--;
}
});