Hi all and welcome back! Welcome back to me too as I’ve been away for a while. Let’s just say I was enjoying a summer vacation from blogging. But I’m back to finish this MEAN series! This week I’ve got AngularJS for you. Maybe next week too.
And in case you need a refresher, here are my previous posts about MEAN:
- MEAN web development #1: MEAN, the what and why
- MEAN web development #2: Node.js in the back
- MEAN web development #3: More Node.js
- MEAN web development #4: All aboard the Node.js Express!
- MEAN web development #5: Jade and Express
- MEAN web development #6: AngularJS in the front
- MEAN web development #7: MongoDB and Mongoose
- MEAN web development #8: Sockets will rock your socks!
- MEAN web development #9: Some last remarks
So in the previous post we’ve seen how we can build pages using the Jade template engine. Pretty sweet, but we need something bigger, better and badder for our front-end.
You can find the examples for this blog on my GitHub page in the mean6-blog repository.
What is AngularJS?
You may have heard of AngularJS before. It’s one of the most popular open-source front-end JavaScript frameworks for the web developed by Google. And, of course, it’s the A in MEAN. But what does it do?
AngularJS is an MVVM framework, much like Knockout.js. It does a bit more than Knockout.js does though. Next to bindings AngularJS can be used for DOM manipulation, more like jQuery. And it does even more, like handling AJAX and routing. As Google likes to put it: AngularJS is “Superheroic” in that it does just about everything.
So instead of talking let’s see some action! First of all we need to install AngularJS. You can download it from the AngularJS website, or you can install it through a package manager such as npm or Bower (install angular). I’ve discussed all three methods in earlier posts so I will not repeat them here. Anyway, if you’ve downloaded my samples from GitHub you’ll be good to go.
The first examples of this post can be tested using nothing but the file system. For later examples with AJAX we’re going to need a little Node.js server, so I’ll add that later. The non-server examples can be found in the front-end.html and the front-end.js files.
So let’s take a look at a first example.
<html>
<head>
<meta charset="utf-8">
<title>AngularJS example</title>
<script src="node_modules/angular/angular.min.js"></script>
</head>
<body ng-app>
<p>This is your first angular expression: {{ 'This is AngularJS' + ' syntax!' }}</p>
</body>
</html>
So there are two things going on here. First is the ng-app directive in the body element. This tells AngularJS that body is the root element of our application and that AngularJS should do its magic. You can place it anywhere you want (like in the html element, or maybe a div element somewhere) and a page can have multple ng-app directives (which I won’t be doing in this post).
Next is, of course, the weird {{ }} syntax, which is the syntax AngularJS uses for its bindings. In this case you’ll see that ‘This is AngularJS’ and ‘ syntax!’ are, indeed, appended in your browser, like it was just some JavaScript. Try using {{ 1 + 2 }} and you’ll see it will print ‘3’ since 1 + 2 equals 3 in JavaScript (and not ’12’).
Now let’s look at something really very cool. Suppose you want to bind some value to an input. Here’s how to do it.
<body ng-app>
<p>Enter you name:
<input type="text" ng-model="firstName" />
<input type="text" ng-model="lastName" />
</p>
<p>You have entered: {{ firstName + ' ' + lastName }}</p>
</body>
No JavaScript required! Wow, that is so cool! And firstName and lastName are updated real time, while you’re typing! We bound our inputs using the ng-model directive which takes care of creating and binding the firstName and lastName properties.
Enter controllers
You’ll often want more control over your code and putting all of your JavaScript into your HTML is not a good idea. So we’ll want to use AngularJS with some custom JavaScript file that we wrote. This is where things get tricky. Not very tricky, but you just got to know how it works.
An AngularJS application is defined by modules. Modules then define controllers.
angular.module('fullNameApp', [])
.controller('fullNameController', function ($scope) {
$scope.firstName = '';
$scope.lastName = '';
$scope.fullName = function () {
return $scope.firstName + ' ' + $scope.lastName;
};
});
So as we see here we create a module by calling the angular.module function and passing it more than one parameter. This returns an application so we can call the controller function directly on the return value. In the controller function we pass in the name of the controller, so we can use it in our HTML, and a constructor function, which receives a $scope variable to which we can append properties.
Now our HTML would look like this:
<html>
<head>
<meta charset="utf-8">
<title>AngularJS example</title>
<script src="node_modules/angular/angular.min.js"></script>
<script src="front-end.js"></script>
</head>
<body ng-app="fullNameApp">
<div ng-controller="fullNameController">
<p>Enter you name:
<input type="text" ng-model="firstName" />
<input type="text" ng-model="lastName" />
</p>
<p>You have entered: {{ fullName() }}</p>
</div>
</body>
</html>
So as you can see we’ve now named our ng-app directive and we’ve added a div element with an ng-controller directive which points to our fullNameController controller. Finally, we now use the fullName function. Notice that we could now set default values in our controller and they’ll be displayed on our page automatically.
$scope.firstName = 'Sander';
$scope.lastName = 'Rossel';
More directives
So let’s take a look at some more directives that can help you build amazing pages. ng-repeat can be used to repeat an element for every item in a list. So let’s add a little array on our controller.
$scope.favoriteMovies = [
'Star Wars',
'Lord of the Rings',
'Fight Club'
];
And display it in an unordered list.
<ul>
<li ng-repeat="movie in favoriteMovies">
{{ movie }}
</li>
</ul>
Now we want to be able to add and delete items from the list. This next piece might blow your mind, but there’s a very simple directive to make a text input that can make a comma separated list and convert it to an array real time.
<input type="text" ng-model="favoriteMovies" ng-list />
So we bind the input to our favoriteMovies using ng-model and then use ng-list to convert it to a comma separated list. Try adding “, Pulp Fiction” (or whatever movie you like) to the text input and the movie will automatically be added to the unordered list we had before!
And if you want something else instead of a comma specifiy it in the ng-list, like so:
<input type="text" ng-model="favoriteMovies" ng-list=" | " />
And what if we add objects instead of strings?
$scope.favoriteAlbums = [
{ artist: 'The Beatles', title: "Sgt. Pepper's Lonely Hearts Club Band" },
{ artist: 'Moby', title: 'Play' },
{ artist: 'The Prodigy', title: 'Fat Of The Land' }
];
<ul>
<li ng-repeat="album in favoriteAlbums">
{{ album.artist + ' - ' + album.title }}
</li>
</ul>
So how about making that editable?
<div ng-repeat="album in favoriteAlbums">
<input type="text" ng-model="album.artist" />
<input type="text" ng-model="album.title" />
</div>
<button ng-click="favoriteAlbums.push({})">New album</button>
And that’s where we see the ng-click in action. Of course we could’ve called a function on our controller too.
$scope.addAlbum = function () {
$scope.favoriteAlbums.push({});
};
<button ng-click="addAlbum()">New album</button>
There’s a little problem with ng-repeat that isn’t quite obvious from these examples. ng-repeat creates a separate scope for each object in an array. For objects this is no problem, but if you were binding to an array of primitives, such as integers or strings, the values wouldn’t be updated. So just remember to use objects when wanting to update array elements.
So how about adding a little styling to our page? With the ng-class directive we can add styles to elements based on some boolean value. The best part is you can add multiple classes based on one or more boolean values. So I have added a little embedded CSS to our page.
<style>
.colored {
color: red;
}
.underlined {
text-decoration: underline;
}
</style>
And two properties in the controller to specify whether we want some text to be colored and/or underlined.
$scope.addColor = true;
$scope.addUnderline = false;
Now in our HTML we can add two checkboxes for the two properties above and then add an ng-class directive on some element that adds the CSS classes based on the JavaScript properties.
Color: <input type="checkbox" ng-model="addColor" />
Underline: <input type="checkbox" ng-model="addUnderline" />
<p ng-class="{ colored: addColor, underlined: addUnderline }">This text might be colored and/or underlined!</p>
Pretty sweet, right? As you can see ng-class should simply evaluate to an object where each property is a class name with a value true or false to specify whether it should be applied.
But there’s an alternative. We could simply specify a string too. So consider the next JavaScript function which returns a string:
$scope.getClasses = function () {
var classes = '';
if ($scope.addColor) {
classes += 'colored ';
}
if ($scope.addUnderline) {
classes += 'underlined ';
}
return classes;
};
We can now use ng-class as follows:
<p ng-class="getClasses()">This text might be colored and/or underlined!</p>
Or you could return an array where each element is either an object such as in the first method or a string such as in the second method. I’ll leave that as practice for the reader though.
Also fun to mention, when you’re inside an ng-repeat directive you can use ng-class-even and ng-class-odd which work exactly as ng-class, but apply the styles only to even or odd elements.
Filters
AngularJS had a feature called filters. It can format values or actually filter lists.
Let’s go back to the first example. Let’s suppose you wanted to show full name in just uppercase or in just lowercase. This is an easy task!
<p>You have entered: {{ fullName() | uppercase }}</p>
<p>You have entered: {{ fullName() | lowercase }}</p>
We can also use a filter to format numbers and dates. It looks kind of the same, except this time you throw in a format.
<p>
<input type="text" ng-model="number"><br>
Number (default): {{ number | number }}<br>
Number (no fractions): {{ number | number: 0 }}<br>
Number (three fractions): {{ number | number: 2 }}
</p>
<p>
Date (default): {{ date | date }}<br>
Date (dd-MM-yyyy): {{ date | date: 'dd-MM-yyyy' }}<br>
Date (yy/M/d): {{ date | date: 'yy/M/d' }}<br>
Date (full): {{ date | date: 'fullDate' }}<br>
Date (long): {{ date | date: 'longDate' }}
</p>
And for arrays you can do some awesome stuff too! For this we use the orderBy or filter filter.
<h3>Ordered by title</h3>
<ul>
<li ng-repeat="album in favoriteAlbums | orderBy: 'title'">
{{ album.artist + ' - ' + album.title }}
</li>
</ul>
<h3>Ordered by artist reverse</h3>
<ul>
<li ng-repeat="album in favoriteAlbums | orderBy: 'artist' : true">
{{ album.artist + ' - ' + album.title }}
</li>
</ul>
<h3>Filtered on everything with '*y*'</h3>
<ul>
<li ng-repeat="album in favoriteAlbums | filter: 'y'">
{{ album.artist + ' - ' + album.title }}
</li>
</ul>
<h3>Filtered on artist with '*y*'</h3>
<ul>
<li ng-repeat="album in favoriteAlbums | filter: { artist: 'y' }">
{{ album.artist + ' - ' + album.title }}
</li>
</ul>
Keep in mind that we can get these values from our JavaScript controller as well. You can make the most awesome dynamic filters with very little trouble. Just make sure you pass in an object with the same properties as the objects you’re repeating and set their values to the values you’d like to filter.
AJAX with AngularJS
So as mentioned AngularJS does a lot more than just HTML binding. One feature we’re going to look at here is that of the $http service. Needless to say we’ll need a little back-end server to communicate with, so for the AJAX examples I’m going to create a Node.js server and some new HTML and JavaScript so we can serve them up using our Node.js server.
Here’s the server:
var express = require('express');
var bodyParser = require('body-parser');
var app = express();
var books = [
{ title: 'Lord of the Rings', author: 'J.R.R. Tolkien' },
{ title: 'Harry Potter', author: 'J.K. Rowling' },
{ title: "The Hitchhiker's Guide to the Galaxy", author: 'Douglas Adams' }
];
app.use(bodyParser.json());
app.use(express.static('public'));
app.get(['/', '/index'], function (req, res) {
res.sendFile(__dirname + '/public/ajax-example.html');
});
app.get('/books', function (req, res) {
res.send(books);
});
app.post('/addBook', function (req, res) {
var book = req.body;
books.push(book);
res.send(books);
});
var server = app.listen(80, '127.0.0.1');
So there’s a lot going on there. First of all I’ve added some Express. I’m also requiring body-parser (npm install body-parser), which is needed to get our POST data. Then I call the app.use function a couple of times. We’ve seen it before. It simply adds a middleware to a path. In this case we tell it to parse any JSON body so we can use it in our app. We also tell it that we can serve static files from the public folder (so we can serve the HTML and JavaScript file).
After that we serve the page by browsing to the root or root/index. I’ve also specified a GET for root/books, which simply returns a list of books (as JSON). And, what it’s all about, a POST to add a book to the list of books.
Let’s look at our front-end JavaScript.
angular.module('ajaxApp', [])
.controller('ajaxController', function ($scope, $http) {
$scope.newAuthor = null;
$scope.newTitle = null;
$scope.books = [];
$scope.getBooks = function () {
$http.get('http://localhost/books')
.then(function (response) {
$scope.books = response.data;
}, function (response) {
alert('Something went wrong while getting the books!');
});
};
$scope.addBook = function () {
$http.post('http://localhost/addBook', { author: $scope.newAuthor, title: $scope.newTitle })
.then(function (response) {
$scope.newAuthor = null;
$scope.newTitle = null;
$scope.books = response.data;
}, function (response) {
alert('Something went wrong while adding a new book!');
});
};
});
So that’s quite a thing too! First of all notice a $http parameter being passed to the controller constructor function. We’ll need this $http parameter to make HTTP calls. Now we first use this in the getBooks function. You’ll see that using this $http stuff is actually very simple! We use $http.get and pass it our URL to get the books. It returns a promise, which has a then function that takes two callbacks, a success function and a failure function. The functions are executed once the asynchronous call returns (AJAX is asynchronous, remember?). So if everything goes right we simply assign the data (a list of books) to the books property. If something goes wrong we show an alert.
In the addBook function I’m using the $http.post function. It’s really similar to the get example, except we’re now passing in some data, a new book. Upon success the book list, including the new book, is returned and we reset the newAuthor and newTitle (nice example of two-way binding by the way).
Now for the HTML:
<html>
<head>
<meta charset="utf-8">
<title>AngularJS AJAX example</title>
<script src="angular.min.js"></script>
<script src="ajax-example.js"></script>
</head>
<body ng-app="ajaxApp">
<div ng-controller="ajaxController">
<h2>AJAX example</h2>
<button ng-click="getBooks()">Get books</button>
<ul>
<li ng-repeat="book in books">
{{ book.author + ' - ' + book.title }}
</li>
</ul>
<input type="text" ng-model="newAuthor" />
<input type="text" ng-model="newTitle" />
<button ng-click="addBook()">Add book</button>
</div>
</body>
</html>
And there you have it!
So AngularJS can do two-way binding, supports MVVM and MVC architecture, it can do AJAX, but also routing, internationalization and localization, you can write custom directives and customize all you like, it supports testing and it has lots of directives I haven’t discussed like ng-show, ng-hide, ng-form, ng-blur… I guess Google wasn’t exaggerating when they called AngularJS ‘superheroic’ because it really seems to have some super powers!
Happy coding!
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