Picking up Angular

What you will learn

What AngularJS is for, and what makes it a good choice for building web apps
How to get up and running quickly with angular using Yeoman and bower
How to use the basic angular concepts of directives, controllers, services and filters to create a web app that can talk to a real RESTful api backend.
Along the way we’ll touch on some of the more advanced angular concepts that you’ll want to be aware of so you can look them up later when you need them.

What makes AngularJS great?

AngularJS is part of a new breed of Javascript MVC frameworks that bring order to the chaotic world of heavily interactive web applications. Writing large web apps in jQuery alone simply becomes a twisted mess of callbacks and dom manipulation. These new MVC frameworks are a recognition that separation of concerns is a good idea if you want to build something maintainable.

Angular distinguishes itself from other javascript MVC frameworks like Backbone.js and Ember.js by taking a completely different perspective on how to do the view. Simply put, Angular doesn’t parse a template string and then insert it into the DOM with innerHTML, instead it let you use custom html tags, attributes, and classes to extend the behavior of HTML. The result is that you can create a completely declarative (logic free) view and have your controllers perform the logic without touching the DOM. This splitting up of responsibilities makes them much more testable and maintainable.

Getting Started

In this tutorial we’re going to create a barebones Twitter-like application called Pipr. Pipr allows you to create “pips” which are short 100 character or less “pips” that show up on the page in reverse chronological order. You can add tags to your pips, and you can post them with any name you like. In addition, you can delete your pips.

The rest of this tutorial assumes you have nodejs installed on your computer. Instructions for installing it can be found at nodejs.org, or you can install it from your operating system’s package manager.

Next, we want to install yeoman. Yeoman is a great tool for streamlining your javascript development workflow, and they have an excellent AngularJS plugin. First, install yeoman with npm:

$ npm install -g yo

Then, you’ll want to create your project directory and initialize your angular project. We’ll call the directory pipr. You can name it whatever you want, but yeoman uses the directory name to name the App itself, so you may have to tweak some of the examples if you call your directory something else.

$ mkdir pipr
$ cd pipr
$ yo angular

This will ask us a few questions.

[?] Would you like to include Twitter Bootstrap? (Y/n)

We do want twitter bootstrap, so say yes to this.

[?] Would you like to use the SCSS version of Twitter Bootstrap with the Compass CSS Authoring Framework? (Y/n)

While SCSS is a great CSS authoring tool, it isn’t what we’re focusing on in this tutorial, just say No for now.

On the next question, you’ll use spacebar to de-select cookies and sanitize, then hit enter when you’re done.

[?] Which modules would you like to include? 
 ⬢ angular-resource.js
‣⬡ angular-cookies.js
 ⬡ angular-sanitize.js

This will install a lot and then create the scaffolding for your project. Here are the files we care about at the moment:

app/scripts
├── app.js
└── controllers
    └── main.js
app/views
└── main.html
app/styles
└── main.css
index.html

To check that everything is working, do:

$ grunt server

That will start a small nodejs server that will serve up your app on localhost:9000 and will auto-refresh when you change any files. This great! Yeoman has done a ton of gruntwork for us, and we can get straight to the good stuff now. Let’s open up app/views/main.html, then delete everything inside it. Now we can begin seeing where angularjs shines: declarative views.

<div class="hero-unit">
  <h1>Pipr</h1>
  <div ng-repeat="pip in pips">
    <pip current-pip="pip" class="well">
      <b>{{pip.name}}</b><br/>
      <i>{{pip.pip}}</i>
    </pip>
  </div>
</div>

There’s a lot going on here, but I bet, even without knowing Angular, you can kind of see what it is trying to do. For every pip in some kind of list of pips, we render the pip name in bold and the pip text in italics. Angular uses the common “{{}}” syntax for templates, with the exception that your template must be valid html! This is because it gets rendered by your browser before angular gets its hands on it. So use “{{}}” syntax only inside text, not across tags etc.

What is this <pip> tag though? That isn’t a part of html, how can that be legal? And what does the pip tag mean? That’s where Angular comes in. Let’s go into app/scripts/controllers/main.js and start looking around.

'use strict';

angular.module('piprApp')
  .controller('MainCtrl', function ($scope) {
    $scope.awesomeThings = [
      'HTML5 Boilerplate',
      'AngularJS',
      'Karma'
    ];
  });

Yeoman has done a lot for us we can see. As we noted before, it’s automatically named our application ‘piprApp’ based on the directory name. This file defines what’s called a controller in Angular. Controllers are where the bulk of your logic should be. Controllers never muck with the DOM, they simply talk to the model, and the view talks to the controller. In Angular, we keep our models in the $scope object, which angular passes to us here. Scopes are hierarchical in Angular, and each controller creates a new one. Angular also watches for changes to attributes of the scope.

Anything we need from Angular, we just ask for in the arguments to the controller, and Angular gets them to us using dependency injection. It’s almost like magic. This is pretty nice and frees us from having to worry about how to get what we need, and whether it’s visible etc. Just ask Angular, and it hands it to you. Below, we’ll ask for the $scope object, and Angular will inject it.

Go ahead and alter the main.js file so it looks like this:

'use strict';

angular.module('piprApp')
  .controller('MainCtrl', function ($scope) {
    // $scope is magically injected by angular, just because we named the argument $scope
    $scope.pips = [
     {id: 1, name: 'Jim', pip: 'Celebrity gossip is crucial to life success...'},
     {id: 2, name: 'Barry', pip: 'Just ate breakfast. Going to watch TV'}
    ]
   });

For now, we’ve added some fake pips to use as an example. We don’t yet know where the <pip> tag is coming from, but now we’ve defined the pips collection we iterate over. Controllers define the behavior we want, and set up the models. You’ll also note that our model is just a plain of javascript object. We don’t need to wrap our model or subclass anything, we can use whatever we want. This is especially cool when we start talking to the server because we can use exactly what the server gives us as our model, and send it right back to them without having to do a bunch of transformations (that is, assuming the server sends JSON).

Directives

If you went to go check your browser to see what happened, you’ll notice that we’re getting our pips showing up, but it looks a bit funky/broken. We’ll fix that next by defining what our <pip> tag does. We do this by creating what Angular calls a “directive”. Directives are great because they allow us to extend the functionality of html by making certain attributes and tags do special functionality. Directives give us the power to bend html to our will, while leaving our controllers free from DOM manipulation and our view (the html) free from inline javascript needed for functionality.

Yeoman allows us to create directive boilerplate quickly, and will wire it up in our app for us. To create our pip directive, you just need to do:

$ yo angular:directive pip

This will create a new directory app/scripts/directives and a new file in there called pip.js. Open that up and check it out (I’ll omit the ‘use strict’ from here on out for brevity, but you should always have it at the top of every file):

angular.module('piprApp')
  .directive('pip', function () {
    return {
      template: '<div></div>',
      restrict: 'E',
      link: function postLink(scope, element, attrs) {
        element.text('this is the pip directive');
      }
    };
  });

This isn’t too far from what we want. Let’s modify it a little bit and then I’ll explain what all these parts mean!

angular.module('piprApp')
  .directive('pip', function () {
      return {
          restrict: "E",
          transclude: true,
          scope: {
              pip: "=currentPip"
          },
          template: '<div ng-transclude id="{{pip.id}}" class="pip-box"></div>',
          replace: true
      };
  });

All this directive does is set the html id to the pip id from the server, and automatically sets the .pip-box class on the div.

First off, our directive returns what’s called a Directive Definition Object, each attribute we use here is important, as they all have defaults, which we’ve overridden for a reason.

restrict:"E" means that this directive is looking for html elements named the same thing as the directive is named. Here the directive is named “pip”, so it’s looking for html tags called <pip>. We could have restricted it to “A” for attribute, or “C” for class also (or any combination like “AE”).

transclude is the next attribute, and despite its scary sounding name, it’s a pretty simple concept. Normally, the directive wipes out the contents of the tag it is activated on, and replaces it with the template. Transclusion allows us to put those contents wherever we want in our template instead of throwing them away. For example if we have in our html:

<pip>Test</pip>

A directive without transclusion renders this to:

<pip><div></div></pip>

Whereas with transclusion on, we would get:

<pip><div>Test</div></pip>

Next, we have the scope attribute. By default, directives have the scope of wherever they happen to be dropped in the html. This can be an issue since the directive really can’t count on the scope having what it needs (although it could put it there if it needed to). By setting the scope attribute to an object, we’re telling Angular to create what’s called an isolate scope. All it means is that each instance of this directive plopped into your html will get its own scope which doesn’t inherit from the outer scope it happens to be in. In order to set up our pip tag, we need to give it a pip object, and we get that object from the syntax:

{ pip: '=currentPip'}

That allows us to pass in the pip like this:

<pip currentPip="aPipFromTheCurrentScope">

The ‘=’ syntax means we get a two-way binding to a property of the outer scope. Normally, the isolate scope locks out all the variables from the outer scope, so we do this so that the user of the pip directive can tell it which object to use as the pip.

Just remember: the directive is totally blind to where it is in the DOM. It’s a reusable component that doesn’t know what controller it will end up in, and it doesn’t know what properties are defined in whatever scope you’ve plopped it into. The best way to tell a directive what is going on is to pass it things it needs as attributes.

The template attribute is fairly straightforward, it’s what to put into the directive. You can see the ng-transclude attribute in use, that’s how angular knows where to put the original contents. You can also see we can refer to the pip object we’ve been passed in from the outside world.

Finally, the replace attribute tells angular not to put our template inside of the <pip> tag it found in the html, but rather to replace it entirely.

Services

Go back to the browser and check it out. That looks good, but if we want to be useful, we’ll need to hook it up to a some kind of real backend. The server backend is something we may need access to in lots of different parts of the application, so the best way to expose it is to create what Angular calls a service.

To create a service, go back to the command line and do:

$ yo angular:service Pipbackend

That will create a directory called app/scripts/services/ along with a file called Pipbackend inside it. That’s where we’ll define our service. Open up that file and make it look like the following:

angular.module('piprApp')
  .service('Pipbackend', function Pipbackend($resource) {
      this.pips = $resource('http://pippypips.herokuapp.com/api/pips/:id');
  });

Briefly, what we’ve done here is use the $resource service provided by angular-resource to make an object that communicates to our preferred backend. Now, if any part of our app wants to talk to the backend, they just have to ask for Pipbackend. If the url of the backend changes, we only have to change it in one place. If we want to do testing without hitting the backend, we can replace the service with a dummy backend, and none of the other code needs to change.

There is one extra step we need to do to make this service work for us, which is to add ngResource as a dependency for our module. We didn’t create the app/scripts/app.js file, yeoman did, but we need to alter it now to add a dependency (this is the top level file, and where routes are declared, but don’t worry about that for now). Make app.js look like this:

angular.module('piprApp', ['ngResource']) // only this line changes
  .config(function ($routeProvider) {
    $routeProvider
      .when('/', {
        templateUrl: 'views/main.html',
        controller: 'MainCtrl'
      })
      .otherwise({
        redirectTo: '/'
      });
  });

This file is why our main.html file is so clean. The index.html file has got all of the boilerplate stuff in it, and it has a small container that our piprApp populates.

Now that we’ve got our backend connection, we need to change our MainCtrl controller to use that backend instead of the fake pips we had before. Go back into app/scripts/controllers/main.js and edit it like so:

angular.module('piprApp')
    .controller('MainCtrl', function ($scope, Pipbackend) {
        $scope.pips = Pipbackend.pips.query({limit: 10, offset: 0});
    });

This is the magic of dependency injection. We just ask for the Pipbackend, and Angular gives it to us, no questions asked. The query() method comes from the $resource module that our Pipbackend uses. It queries for all of the pips on the server, with the paging criteria we give it.

Getting Input from the User with ngModel

Since we can now list pips from the server, the next thing we need to do is be able to create new pips of our own. Let’s add the html for that back in apps/views/main.html right above where we list all of the pips:

...
  <h1>Pipr</h1>
  <form name="pipForm">
    <input type="text" ng-model="newPip.name" placeholder="Name"/><br />
    <textarea ng-model="newPip.pip" placeholder="pip up here..."/>
    <b>{{100 - newPip.pip.length}}</b>
    <button ng-click="makePip()"
            class="btn btn-success">Post Pip</button>
  </form>
  <div ng-repeat="pip in pips">
...

There is some new stuff here. ng-model is a convenient directive provided by Angular that lets us hook a form element right up to the current scope. Angular defines special directives for all html form controls, so we don’t have to manually add keypress listeners, or access the text attribute directly, or any of that. Also, if the “newPip” variable isn’t already in our current scope, ngModel creates it for us.

ngModel is an example of a directive that triggers off an attribute (restrict: A), rather than being a tag like our <pip> tag was. The other new thing you’ll notice is ng-click on the post button. This calls a function on the current scope. We haven’t written makePip yet, but we’ll do that next.

Note: You may have noticed that we play fast and loose with attribute names like ‘ng-model’ becoming a directive called ‘ngModel’. That’s because Angular normalizes all of these names from the html when we use them in the Javascript. So for example, ‘ng-model’, ‘ngModel’, ‘ng:model’, ‘x-ng-model’ and ‘data-ng-model’ are all equivalent. That allows us to use the conventions of html and say ‘current-pip’, but in the Javascript we can use Javascript conventions and refer to ‘currentPip’.

You can try out the new form field in your browser. The countdown will work when you type in the pip field, but the post button won’t do anything since we haven’t hooked it up. Let’s go back to the MainCtrl again in app/scripts/controllers/main.js again and add the functionality we need.

angular.module('piprApp')
    .controller('MainCtrl', function ($scope, Pipbackend) {
        $scope.refreshPips = function(){
            Pipbackend.pips.query(
                {limit: 10, offset: 0},
                function(pipList){$scope.pips = pipList}
            );
        };
        $scope.makePip = function(){
            Pipbackend.pips.save($scope.newPip, function onSuccess(newPip){
                $scope.newPip = {name: $scope.newPip.name};
                $scope.refreshPips();
            });
        };
        $scope.refreshPips();
  });

This does a couple of new things. First, we made a function on the scope that refreshes the list of pips from the server. The scope is the right place to define functions like this. This function sets the $scope.pips value once the request is successful. We could have done something like this:

$scope.pips = Pipbackend.pips.query(...);

This will work, because the query function from ngResource returns an empty object that it will populate automatically once the server responds. The problem is that this causes the pip list to flash since we empty it out while the server response is happening. Setting the new value in the callback keeps everything smooth.

Also worth noting is that we clear out the $scope.newPip variable when saving, but keep the name the same so the user doesn’t have to retype it.

Validation

Now we can create pips and post them to the server, but there are some rules about the pips we’d like to enforce so that the server doesn’t yell at us. The first rule is that a pip must be at most 100 characters long. Also, both the name and pip fields must have something in them. So let’s add that constraint to the form using Angular’s validation directives. We’ll go into the app/views/main.html and modify those two inputs like this:

...
<input type="text" required ng-model="newPip.name" placeholder="Name"/><br />
<textarea ng-maxlength="100" required ng-model="newPip.pip" placeholder="pip up here..."/>
...

In addition, we should enable or disable the post button based on whether the form is valid currently. Do that so:

...
<button ng-click="makePip()"
        ng-disabled="pipForm.$invalid || pipForm.$pristine"
        class="btn btn-success">Post Pip</button>
...

If you try it out in the browser, you’ll see that the button is disabled until we fill in both fields, and if we type more than 100 characters into the pip field, the button becomes disabled again. Neat and simple!

There are more rules that the server uses to decide if an instance is valid, and we could codify them all using angular validation, but inevitably there will be some problems reported by the server that your client won’t be able to prevent. Things like two users editing at the same time etc. Let’s add an error box to report server errors. First edit main.html again to add the actual box right after our form:

...
</form>
  <div class="alert alert-error" ng-show="error">{{error}}</div>
<div ng-repeat="pip in pips">
...

This will hide the alert when there is no error. Then add a failure callback to makePip in main.js:

$scope.makePip = function(){
    Pipbackend.pips.save(
        $scope.newPip,
        function onSuccess(newPip){
            $scope.newPip = {name: $scope.newPip.name};
            $scope.refreshPips();
            $scope.error = null;
        },function onFailure(response){
            $scope.error = response.data.error;
        });
};

To test this out, try posting with a name longer than 100 characters.

Finishing Touches

There are a few last things we’d like to add to our app.

The ability to add tags to pips, and show them
The ability to delete pips
Show the creation date of the pips

Here’s the final version of main.html:

<div class="hero-unit">
  <h1>Pipr</h1>
  <form name="pipForm">
    <input type="text" required 
           ng-model="newPip.name" placeholder="Name"/><br />
    <textarea ng-maxlength="100" required
              ng-model="newPip.pip" placeholder="pip up here..."/>
    <b>{{100 - newPip.pip.length}}</b>
    <input type="text"
           ng-model="newPip.tags" split-to-list />
    <button ng-click="makePip()"
            ng-disabled="pipForm.$invalid || pipForm.$pristine"
            class="btn btn-success">Post Pip</button>
  </form>
  <div class="alert alert-error" ng-show="error">{{error}}</div>
  <div ng-repeat="pip in pips">
    <pip current-pip="pip" class="well">
      <a class="close" ng-click="deletePip(pip.id)">&times;</a>
      <b>{{pip.name}}</b>  <br>
      <i>{{pip.pip}}</i>   <br ng-show="pip.tags">
      <span ng-repeat="tag in pip.tags" class="label label-inverse">
        {{tag}}
      </span>
      <br>@ {{pip.created | date:'medium'}}
    </pip>
  </div>
</div>

You can see a couple of new things here. First is the filter we use when displaying the date. Filters are applied using the ‘|’ character, and Angular comes with some useful filters built in like uppercase, date, and currency. Here we use the date filter with an argument of ‘medium’ to show a human readable version of the pip creation date.

We also added a delete button to every pip. You can see that when it’s clicked, the deletePip function will be called with the current pip’s id. We’ll write that function in a bit.

The next interesting thing to notice is that we added an input for the tags from the user. The server, only accepts tags as a list of strings, so we need to split the raw input from the user before putting it into the model, and this is what the splitToList directive does. That isn’t a built-in directive however, so we need to write it. Let’s do that now:

$ yo angular:directive splitToList

Then open up app/scripts/directives/splitToList.js and add the following:

angular.module('piprApp')
  .directive('splitToList', function () {
      return {
        restrict: 'A',
        require: 'ngModel',
        link: function (scope, element, attrs, ngModelCtrl) {
            ngModelCtrl.$parsers.push(function(text){
                return text.split(' ');
            });
        }
    };
  });

This is a completely different kind of directive than we made before. It’s an attribute directive, and it has a requirement that an ngModel directive already be applied on the element we’re working on. Adding this require property also makes it so the ngModel controller is passed to our linking function.

What’s a linking function? Simply put, it gets called after our directive is applied and lets us set things up for the directive. Here, all we want to do modify the ngModel’s list of parsers. The parsers are all applied in order to the input from the text box before it is added to the model. We add a function that splits on spaces to the end of the pipeline so that our model only ever receives a list of strings.

Finally, let’s add our deletePip function so that we can delete pips that we don’t like. Here’s the final version of our main.js:

angular.module('piprApp')
    .controller('MainCtrl', function ($scope, Pipbackend) {
        $scope.refreshPips = function(){
            Pipbackend.pips.query(
                {limit: 10, offset: 0},
                function onSuccess(pipList){
                    $scope.pips = pipList;
                    $scope.clearError();
                },
                $scope.setError
            );
        };
        $scope.makePip = function(){
            Pipbackend.pips.save(
                $scope.newPip,
                function onSuccess(newPip){
                    $scope.newPip = {name: $scope.newPip.name};
                    $scope.refreshPips();
                },
                $scope.setError
            );
        };
        $scope.deletePip = function(pipId) {
            Pipbackend.pips.delete(
                {id: pipId},
                $scope.refreshPips,
                $scope.setError);
        };
        $scope.setError = function(resp){ $scope.error = resp.data.error};
        $scope.clearError = function(){ $scope.error = null };
        $scope.refreshPips();
  });

In addition to adding the deletePip function, we also tidied up the error handling a bit so that you always know what went wrong. Here’s the final source code tree for what we created:

app/scripts
├── app.js
├── controllers
│   └── main.js
├── directives
│   ├── pip.js
│   └── splitToList.js
└── services
    └── Pipbackend.js
app/views
└── main.html
index.html

Where to Go Next

There’s a lot more we could do to this app to get even more functionality. Here are some suggestions:

Add the ability to page results using the limit and offset parameters to query
Add a text box that filters pips based on their tags or content
Automatically add tags to a pip by parsing the pip body for hash tags
Add a refresh button to refresh the pips from the server

In addition, here are some Angular resources that you’ll want to look into if you’re looking to build a real application:

Angular-UI: http://angular-ui.github.io is a great way to start adding ui functionality to your app
Restangular: https://github.com/mgonto/restangular is a powerful alternative to ngResource. It allows greater flexibility when interacting with RESTful apis.

Finally, the source code for this tutorial, as well as the server code can be found at https://github.com/deontologician/pipr. If you want to deploy your own pipr application on heroku, you can use the code there to do it.

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