AngularJS vs. jQuery

AngularJS and jQuery adopt very different ideologies. If you're coming from jQuery you may find some of the differences surprising. AngularJS may make you angry.

This is normal, you should push through. AngularJS is worth it.

The big difference (TLDR)

jQuery gives you a toolkit for selecting arbitrary bits of the DOM and making ad-hoc changes to them. You can do pretty much anything you like piece by piece.

AngularJS instead gives you a compiler.

What this means is that AngularJS reads your entire DOM from top to bottom and treats it as code, literally as instructions to the compiler. As it traverses the DOM, It looks for specific directives(compiler directives) that tell the AngularJS compiler how to behave and what to do. Directives are little objects full of JavaScript, and can match attributes, tags, classes or even comments. These directives can then in turn pull in additional Angular components.

Meanwhile it wires up your DOM with all sorts of useful goodness that will make your day brighter and will make your clients smile. What comes out the bottom of the compiler is a fully formed web application, wired up and ready to go.

Your template drives the JavaScript, not the other way around. This is a radical reversal of roles that can take some getting used to.

If this sounds like it might be over-prescriptive and limiting, nothing could be farther from the truth. Because AngularJS treats your HTML as code, you get HTML level granularity in your web application. Everything is possible, and most things are surprisingly easy once you make a few conceptual leaps.

Let's get down to the nitty gritty.

First up, AngularJS doesn't replace jQuery

AngularJS and jQuery do different things. AngularJS gives you a set of tools to produce web applications. jQuery mainly gives you tools for modifying the DOM. If jQuery is present on your page, AngularJS will use it automatically. If it isn't, AngularJS ships with jQuery Lite, which is a cut down, but still perfectly usable version of jQuery.

Misko likes jQuery and encourages you to use it. You sometimes still need to manipulate the DOM directly and jQuery is a friendly tool for this. However you can get a pretty much all of your work done using a combination of scope, templates and directives, and you should prefer this workflow where possible because your code will be more discrete, more configurable, and more Angular.

People encouraging you to drop jQuery altogether should stop encouraging you to do that. You probably ought to lay off the jQuery for a while while you learn what AngularJS can do, but jQuery is not going away just yet.

That said, you shouldn't be sprinkling jQuery all over the place. The correct place for jQuery and other DOM manipulations in AngularJS is in directives. More on these later.

Unobtrusive JavaScript with Selectors vs. Declarative Templates

jQuery is typically applied unobtrusively. Your JavaScript code is linked in the header, and this is the only place it is mentioned. We use selectors to pick out bits of the page and write plugins to modify those parts.

The JavaScript is in control. The HTML has a completely independent existence. Onclick attributes are very bad practice.

One of the first things your will notice about AngularJS is that custom attributes are everywhere. Your HTML will be littered with ng attributes, which are essentially onClick attributes on steroids. These are directives (compiler directives), and are one of the main ways in which the template is hooked to the model.

When you first see this you might be tempted to write AngularJS off as old school intrusive JavaScript (like I did at first). In fact, AngularJS does not play by those rules. In AngularJS, your HTML5 is a template. It is compiled by AngularJS to produce your web page.

This is the first big difference. To jQuery, your web page is a DOM to be manipulated. To AngularJS, your HTML is code to be compiled. AngularJS reads in your whole web page and literally compiles it into a new web page using its built in compiler.

Your template should be declarative; its meaning should be clear simply by reading it. We use custom attributes with meaningful names. We make up new HTML elements, again with meaningful names. A designer with minimal HTML knowledge and no coding skill can read your AngularJS template and understand what it is doing. He or she can make modifications. This is the AngularJS way.

The template is in the driving seat.

One of the first questions I asked myself when starting AngularJS and running through the tutorials is"Where is my code?". I've written no JavaScript, and yet I have all this behaviour. The answer is obvious. Because AngularJS compiles the DOM, AngularJS is treating your HTML as code. For many simple cases it's often sufficient to just write a template and let AngularJS compile it into an application for you.

Your template drives your application. It's treated as a DSL. You write AngularJS components, and AngularJS will take care of pulling them in and making them available at the right time based on the structure of your template. This is very different to a standard MVC pattern, where the template is just for output.

It's more similar to XSLT than Ruby on Rails for example.

This is an inversion of control that takes some getting used to.

Stop trying to drive your application from your JavaScript. Let the template drive the application, and let AngularJS take care of wiring the components together. This also is the AngularJS way.

Semantic HTML vs. Semantic Models

With jQuery your HTML page should contain semantic meaningful content. If the JavaScript is turned off (by a user or search engine) your content remains accessible.

Because AngularJS treats your HTML page as a template. The template is not supposed to be semantic as your content is typically stored in your model. AngularJS compiles your DOM with the model to produce a semantic web page.

In AngularJS, meaning lives in the model, the HTML is just a template, for display only.

At this point you likely have all sorts of questions concerning SEO and accessibility, and rightly so. There are open issues here. Most screen readers will now parse JavaScript. Search engines can also index AJAXed content. Nevertheless, you will want to make sure you are using pushstate URLs and you have a decent sitemap. See here for a discussion of the issue:http://stackoverflow.com/a/23245379/687677

Separation of concerns (SOC) vs. MVC

Separation of concerns (SOC) is a pattern that grew up over many years of web development for a variety of reasons including SEO, accessibility and browser incompatibility. It looks like this:

1. HTML - Semantic meaning. The HTML should stand alone.
2. CSS - Styling, without the CSS the page is still readable.
3. JavaScript - Behaviour, without the script the content remains.

Again, AngularJS does not play by their rules. In a stroke, AngularJS does away with a decade of received wisdom and instead implements an MVC pattern in which the template is no longer semantic, not even a little bit.

It looks like this:

1. Model - your models contains your semantic data. Models are usually JSON objects. Models exist as attributes of an object called $scope. You can also store handy utility functions on $scope which your templates can then access.
2. View - Your views are written in HTML. The view is usually not semantic because your data lives in the model.
3. Controller - Your controller is a JavaScript function which hooks the view to the model. Its function is to initialise $scope. Depending on your application, you may or may not need to create a controller. You can have many controllers on a page.

MVC and SOC are not on opposite ends of the same scale, they are on completely different axes. SOC makes no sense in an AngularJS context. You have to forget it and move on.

If, like me, you lived through the browser wars, you might find this idea quite offensive. Get over it, it'll be worth it, I promise.

Plugins vs. Directives

Plugins extend jQuery. AngularJS Directives extend the capabilities of your browser.

In jQuery we define plugins by adding functions to the jQuery.prototype. We then hook these into the DOM by selecting elements and calling the plugin on the result. The idea is to extend the capabilities of jQuery.

For example, if you want a carousel on your page, you might define an unordered list of figures, perhaps wrapped in a nav element. You might then write some jQuery to select the list on the page and restyle it as a gallery with timeouts to do the sliding animation.

In AngularJS, we define directives. A directive is a function which returns a JSON object. This object tells AngularJS what DOM elements to look for, and what changes to make to them. Directives are hooked in to the template using either attributes or elements, which you invent. The idea is to extend the capabilities of HTML with new attributes and elements.

The AngularJS way is to extend the capabilities of native looking HTML. You should write HTML that looks like HTML, extended with custom attributes and elements.

If you want a carousel, just use a <carousel /> element, then define a directive to pull in a template, and make that sucker work.

Lots of small directives vs. big plugins with configuration switches

The tendency with jQuery is to write great big plugins like lightbox which we then configure by passing in numerous values and options.

This is a mistake in AngularJS.

Take the example of a dropdown. When writing a dropdown plugin you might be tempted to code in click handlers, perhaps a function to add in a chevron which is either up or down, perhaps change the class of the unfolded element, show hide the menu, all helpful stuff.

Until you want to make a small change.

Say you have a menu that you want to unfold on hover. Well now we have a problem. Our plugin has wired in our click handler for us, we're going to need to add a configuration option to make it behave differently in this specific case.

In AngularJS we write smaller directives. Our dropdown directive would be ridiculously small. It might maintain the folded state, and provide methods to fold(), unfold() or toggle(). These methods would simply update $scope.menu.visible which is a boolean holding the state.

Now in our template we can wire this up:

<a ng-click="toggle()">Menu</a>  <ul ng-show="menu.visible">    ...  </ul>

Need to update on mouseover?

<a ng-mouseenter="unfold()" ng-mouseleave="  fold()">Menu</a>  <ul ng-show="menu.visible">    ...  </ul>

The template drives the application so we get HTML level granularity. If we want to make case by case exceptions, the template makes this easy.

Closure vs. $scope

jQuery plugins are created in a closure. Privacy is maintained within that closure. It's up to you to maintain your scope chain within that closure. You only really have access to the set of DOM nodes passed in to the plugin by jQuery, plus any local variables defined in the closure and any globals you have defined. This means that plugins are quite self contained. This is a good thing, but can get restrictive when creating a whole application. Trying to pass data between sections of a dynamic page becomes a chore.

AngularJS has $scope objects. These are special objects created and maintained by AngularJS in which you store your model. Certain directives will spawn a new $scope, which by default inherits from its wrapping $scope using JavaScript prototypical inheritance. The $scope object is accessible in the controller and the view.

This is the clever part. Because the structure of $scope inheritance roughly follows the structure of the DOM, elements have access to their own scope, and any containing scopes seamlessly, all the way up to the global $scope (which is not the same as the global scope).

This makes it much easier to pass data around, and to store data at an appropriate level. If a dropdown is unfolded, only the dropdown $scope needs to know about it. If the user updates their preferences, you might want to update the global $scope, and any nested scopes listening to the user preferences would automatically be alerted.

This might sound complicated, in fact, once you relax into it, it's like flying. You don't need to create the $scope object, AngularJS instantiates and configures it for you, correctly and appropriately based on your template hierarchy. AngularJS then makes it available to your component using the magic of dependency injection (more on this later).

Manual DOM changes vs. Data Binding

In jQuery you make all your DOM changes by hand. You construct new DOM elements programatically. If you have a JSON array and you want to put it to the DOM, you must write a function to generate the HTML and insert it.

In AngularJS you can do this too, but you are encouraged to make use of data binding. Change your model, and because the DOM is bound to it via a template your DOM will automatically update, no intervention required.

Because data binding is done from the template, using either an attribute or the curly brace syntax, it's super easy to do. There's little cognitive overhead associated with it so you'll find yourself doing it all the time.

<input ng-model="user.name" />

Binds the input element to $scope.user.name. Updating the input will update the value in your current scope, and vice-versa.

Likewise:

<p>    {{user.name}}  </p>

will output the user name in a paragraph. It's a live binding, so if the $scope.user.name value is updated, the template will update too.

Ajax all of the time

In jQuery making an Ajax call is fairly simple, but it's still something you might think twice about. There's the added complexity to think about, and a fair chunk of script to maintain.

In AngularJS, Ajax is your default go-to solution and it happens all the time, almost without you noticing. You can include templates with ng-include. You can apply a template with the simplest custom directive. You can wrap an Ajax call in a service and create yourself a GitHub service, or aFlickr service, which you can access with astonishing ease.

Service Objects vs Helper Functions

In jQuery, if we want to accomplish a small non-dom related task such as pulling a feed from an API, we might write a little function to do that in our closure. That's a valid solution, but what if we want to access that feed often? What if we want to reuse that code in another application?

AngularJS gives us service objects.

Services are simple objects that contain functions and data. They are always singletons, meaning there can never be more than one of them. Say we want to access the Stack Overflow API, we might write a StackOverflowService which defines methods for doing so.

Let's say we have a shopping cart. We might define a ShoppingCartService which maintains our cart and contains methods for adding and removing items. Because the service is a singleton, and is shared by all other components, any object that needs to can write to the shopping cart and pull data from it. It's always the same cart.

Service objects are self-contained AngularJS components which we can use and reuse as we see fit. They are simple JSON objects containing functions and Data. They are always singletons, so if you store data on a service in one place, you can get that data out somewhere else just by requesting the same service.

Dependency injection (DI) - aka de-spaghettification

AngularJS manages your dependencies for you. If you want an object, simply refer to it and AngularJS will get it for you.

Until you start to use this, it's hard to explain just what a massive time boon this is. Nothing like AngularJS DI exists inside jQuery.

DI means that instead of writing your application and wiring it together, you instead define a library of components, each identified by a string.

Say I have a component called 'FlickrService' which defines methods for pulling JSON feeds from Flickr. Now, if I want to write a controller that can access Flickr, I just need to refer to the 'FlickrService' by name when I declare the controller. AngularJS will take care of instantiating the component and making it available to my controller.

For example, here I define a service:

myApp.service('FlickrService', function() {    return {      getFeed: function() { // do something here }    }  });

Now when I want to use that service I just refer to it by name like this:

myApp.controller('myController', ['FlickrService', function(FlickrService) {    FlickrService.getFeed()  }]);

AngularJS will recognise that a FlickrService object is needed to instantiate the controller, and will provide one for us.

This makes wiring things together very easy, and pretty much eliminates any tendency towards spagettification. We have a flat list of components, and AngularJS hands them to us one by one as and when we need them.

Modular service architecture

jQuery says very little about how you should organise your code. AngularJS has opinions.

AngularJS gives you modules into which you can place your code. If you're writing a script that talks to Flickr for example, you might want to create a Flickr module to wrap all your Flickr related functions in. Modules can include other modules (DI). Your main application is usually a module, and this should include all the other modules your application will depend on.

You get simple code reuse, if you want to write another application based on Flickr, you can just include the Flickr module and voila, you have access to all your Flickr related functions in your new application.

Modules contain AngularJS components. When we include a module, all the components in that module become available to us as a simple list identified by their unique strings. We can then inject those components into each other using AngularJS's dependency injection mechanism.

To sum up

AngularJS and jQuery are not enemies. It's possible to use jQuery within AngularJS very nicely. If you're using AngularJS well (templates, data-binding, $scope, directives, etc.) you will find you need alot less jQuery than you might otherwise require.

The main thing to realise is that your template drives your application. Stop trying to write big plugins that do everything. Instead write little directives that do one thing, then write a simple template to wire them together.

Think less about unobtrusive JavaScript, and instead think in terms of HTML extensions.

http://nicholasjohnson.com/angular-book/. I hope it's helpful.

Listen to the podcast JavaScript Jabber: Episode #32 that features the original creators of AngularJS: Misko Hevery & Igor Minar. They talk a lot about what it's like to come to AngularJS from other JavaScript backgrounds, especially jQuery.

One of the points made in the podcast made a lot of things click for me with respects to your question:

MISKO: [...] one of the things we thought about very hardly in Angular is, how do we provide lots of escape hatches so that you can get out and basically figure out a way out of this. So to us, the answer is this thing called "Directives". And with directives, you essentially become a regular little jQuery JavaScript, you can do whatever you want.

IGOR: So think of directive as the instruction to the compiler that tells it whenever you come across this certain element or this CSS in the template, and you keep this kind of code and that code is in charge of the element and everything below that element in the DOM tree.

A transcript of the entire episode is available at the link provided above.

So, to directly answer your question: AngularJS is -very- opinionated and is a true MV* framework. However, you can still do all of the really cool stuff you know and love with jQuery inside of directives. It's not a matter of "How do I do what I used to in jQuery?" as much as it's a matter of "How do I supplement AngularJS with all of the stuff I used to do in jQuery?"