2016/08/22

React vs AngularJS – How the two Compare



The purpose of this article is to go over building some simple functionality using Angular and React to give you an understanding as to what it would take to get an application off the ground. Angular is the big dog in this fight, as it’s been around for a while longer than React has, but React brings increased rendering performance to the table. This post is not meant as an in-depth tutorial on either of the frameworks. As such, I’m not going to go into great detail for a lot of this stuff.
If you ever feel as though you need more clarification on a topic, either throw me a question viaTwitter or comment below. The documentation for Angular and React is also pretty good. I’m hoping that after you read this, you’ll have a greater understanding as to which framework is right for you to use on your next project. At the very least, you should have a grasp on how JavaScript UI frameworks operate in general.
I’m going to walk through how to create the typical coding example using each of the frameworks. Once I’ve done that, I’ll move on to some more complicated UI controls, building up our little app as we go.
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Hello, world!
Angular JS
  1. First, we’re initializing the Angular app by calling angular.module and giving it a name. The second argument in this call is the list of dependencies our module relies on. Since we don’t have any dependencies, we pass in an empty array.
  1. Next, we’re initializing the testController Angular controller. It’s not doing anything at the moment as our directive is handling all the “heavy” lifting.
  1. Finally, the directive is defined. All it’s doing is writing out a div containing the hello world text.
  1. The html tag has the aforementioned ng-app directive applied to it, indicating that the page reflects an Angular application named “testApp”.
  1. The body tag is annotated with the ng-controller directive, which tells Angular that the controller’s scope should reside within it.
  1. Finally, we’re rendering our hello-world directive as the only code in the body.
React JS
  1. We call React.createClass to (unsurprisingly) create a React class. This class is what gets rendered later on to be appended into an HTML element for the user to interact with.
  1. The createClass function takes an object which needs to contain a render function, which is all that’s in our simple class so far. It returns a very simple JSX string to write out hello world.
  1. The last line of the JSX is used to render our hello world class into the document.body.
Injecting Data
Angular JS
  • Two-way binding: Indicates that changes made on either the parent or child scope are reflected in the other. It’s denoted by an equals sign (=) when building the scope.
  • One-way binding: Data flows only from child to parent via a function. Denoted by an ampersand (&).
  • Text binding. Just a string value that contains no binding information. Denoted by an at symbol (@).
  • The hello-world element in the HTML pane now contains a name attribute, which corresponds to the value defined in our isolated scope.
  • Our controller now has a definition of the name variable in its scope.
  • The directive template now contains a reference to the name scope variable.
  • We’ve added a scope section to our directive definition which indicates that two things: first, that the directive should create an isolated scope, and second that it should contain only the name parameter as defined by the text binding (@). Whenever this scope section exists, an isolated scope is defined.
React JS
  • We’ve added a { name: "Chris Harrington" } to the creation of our HelloWorld class, which gets translated into the props property inside the class.
  • The JSX now includes a reference to this.props.name so we can render a personalized hello message.
Event Handlers
Angular JS
  • We’ve added a button to our directive template, which sets our greeting message on click. It has the ng-click directive set to fire the greet method.
  • The link section to the directive has been added. This section is fired when the directive is rendered and is used to set up things like event handlers and default values, both of which are occurring here. The greeting property has been set to the empty string on the scope, and we’ve added a basic event handler (greet) to handle the button click.
React JS
  • The getInitialState function is used to determine the initial state of the view. Without it,this.state will return null, potentially breaking the view. If you’re going to set any state during the operation of your class, you need to add this method. In our example, we’re just setting the greeting state property to the empty string.
  • We’ve added a greet function to act as the event handler after the user has clicked on the button.
  • Speaking of which, we’ve added a button to the HTML and are using React’s onClick event to hook up the handler, which is the greet function of the context.
Nested Views
Angular JS
  • First, some house keeping. I’ve moved the templates into script tags in our HTML to keep things neat. In our directive initialization, I’m now grabbing the template HTML from these script tags.
  • I’ve added the wrapper directive, too. It’s very simplistic, containing only a div styled with a darker background and some padding on the HTML/CSS side. On the JavaScript side, the directive initialization for the wrapper contains one property that’s not in our hello-worlddirective: the transclude property. This property indicates that any child elements of the directive should be rendered into the template via a built-in Angular directive calledng-transclude. You can see it in the HTML in the wrapper template. You’ll see in thehello-world directive HTML that the wrapper contains children that show our greeting. Those children get rendered into the ng-transclude directive in our wrapper directive.
  • There’s now a CSS class to set the style of the wrapper. Just a background and some padding; nothing fancy.
React JS
  • The Wrapper class comes before the HelloWorld class because it’s required in the HelloWorld‘s render method. It’s not necessary to do it this way, but I like it as it gives a natural order to where your classes sit. The Wrapper‘s render method contains a single div with a CSS class specified to give our wrapper the background and padding. Inside that div is a reference to a special variable: this.props.children. This variable contains all inner elements of the class when rendered in another class. Our HelloWorld class has the important parts of our greeting HTML inside the Wrapper, so that’s what gets rendered as a result of a call to the children props variable.
  • Our HelloWorld class now contains a reference to the Wrapper class so as to provide the wrapping container.
Loops
Angular JS
  • The hello-world directive now has a div after the button which uses the ng-repeat directive. It indicates that the marked div should be repeated for every greeting in the greetings array on the directive’s scope.
  • The greet method on the directive’s scope now adds three separate greetings to the greetings array to be rendered on the view.
React JS
  • The render method in the HelloWorld class has been refactored to reference arenderGreetings method, which renders all the greetings in the state. When I first started building React classes, I was under the mistaken impression that only the render method could contain HTML. That’s definitely not the case.
  • The greet method now pushes three separate greetings onto the greetings state variable.
  • The getInitialState method replaces the previous greeting variable with a new greetingsvariable, which is set to an empty array.
Conclusion
Angular has been around for a while now, with its initial release in 2009. Since then, it’s come a long way, and they’re up to version 1.3.8 now, with semi-regular releases. Lately, there’s been some buzz about Angular 2.0, which is going to change a lot about the framework, but it’s a long way off, and is scheduled for release sometime in 2016. The current Angular version uses various attributes and custom HTML elements to provide functionality on various DOM elements. These are called directives and are very versatile.
The set up code for Angular is a little verbose, as it requires an application and a controller, as well as definitions for any directives you’re building. The snippet above shows how to set up an initial Angular app, then define a controller and finally build a hello world directive. Here’s a breakdown of what we’re doing with the JavaScript.
An Angular app requires that the ng-app and ng-controller directives be set on various elements. Here’s a rundown.
If you’ve never heard of React JS, it’s a performance-minded view renderer made by the Facebook guys. A lot of the heavyweight contenders for MVVM frameworks have a hard time rendering large amounts of data, like in lists and such. React doesn’t have that problem, as it renders only what’s changed. For example, if a user is viewing a list of 100 items rendered with React, and he or she changes the third one down somehow, only that item gets rerendered, leaving the other 99 items unchanged. It also uses what Facebook calls a “virtual DOM” for some increased performance by writing out a full render virtually, and then checking the difference between the virtual render and what’s actually on the DOM and creating a patch. React uses JSX files (optionally) to write views, which means that JavaScript and HTML can live in a single file. It’s a bit of a paradigm shift and takes a little getting used to. You don’t have to use JSX to write React views, but it’s much easier than spelling out which components to render, so I’d suggest using it. If you’d like a little more information on React, I’ve written an in-depth tutorial for it here. It also goes over the Flux data architecture which I won’t be covering here. Note: React classes can be built in one of two ways: in raw JavaScript or in JSX, a language that combines HTML and JavaScript in one file format. I’m using JSX in the JavaScript sections of the examples below. If you’d like some more information, here’s the documentation.
See the Pen pvEYJv by Chris Harrington (@chrisharrington) on CodePen.
React requires that you build a class to define what HTML to render. That’s what we’re doing in the JavaScript section.
The HTML for the React section isn’t noteworthy at all, and won’t change throughout this article, so you can stop looking at it.
The method Angular uses to inject data into directives is via scopes. A scope in the Angular world is just an object which contains data for various controls, like directives and controllers. On top of that, there’s a root scope object (injected with $rootScope) that functions as a top-level scope accessible by all other Angular components. A directive can have one of a few kinds of scope. First, there’s no directive scope, which means that it uses its parent’s scope (usually the controller’s scope). Then, there’s an isolated scope, which indicates that the directive has its own scope completely separate from the controller’s scope. Typically, a controller’s scope is used to inject data into a directive’s isolated scope. In my experience, the isolated scope is what gets used the most. That may have been confusing. The scope documentation should clear any of that up for you. Scope properties come in three different flavours:
Here, we’re using a text binding to send my name into the hello world example.
React injects data into its rendered views at construct time, be that when the root view is created or via a nested view. Inside the class, the data that’s passed in is accessed via theprops property of the current context.
See the Pen emdmJK by Chris Harrington (@chrisharrington) on CodePen.
In Angular, event handlers are typically assigned to various portions of your view via directives. If you hadn’t noticed by now, directives make up a large portion of what makes Angular great. They’re used for practically everything. The ng-click directive is an attribute that can be placed on HTML elements that hooks up a click handler that already exists on the local scope.
See the Pen ZYpExy by Chris Harrington (@chrisharrington) on CodePen.
Event handlers in React work by setting various custom attributes on the HTML elements you’re building. Most of the common culprits have associated handlers.
There’s a few new things we’re introducing here. The big one is the idea of state. Each React class has its own internal state that can’t be modified by external means. You can modify the state of a directive by calling the setState method of the view’s context. Doing so will trigger a rerender of the changed elements. You get the state properties using this.state.name, for example, and you can even set data this way, too, but if you do, a rerender isn’t triggered. A good rule of thumb is that if you’re setting data on the state, use the setState method.
Nested views in Angular are accomplished using multiple directives. One directive can contain a reference to another without any problems. It’s worth noting that each of these directives can have their own isolated scope, and any level of nested directives will also have their own scopes. Angular uses the idea of transclusion to render child elements from a directive. Transclusion is a little complicated, so here’s the documentation if you need it. Here’s a quick example:
See the Pen zxKZGL by Chris Harrington (@chrisharrington) on CodePen.
Here, I’ve created a wrapper directive which (unsurprisingly) wraps our hello-world directive by adding some padding and a gray background colour. So, what’s changed in the code?
Nested elements in React are much easier to put together, at least in my opinion. It’s as easy as declaring the various classes, and then referencing the child class in the render method of the parent class.
Like in the Angular example, we’ve wrapped up the meat of our HelloWorld HTML in a newWrapper class, which again provides a background colour and some padding.
That’s it. There are no more changes for the React side of things. It’s much cleaner than the Angular implementation, in my opinion. If you’d like to read more on React’s implementation of child elements, take a look here.
Both Angular and React provide methods for rendering views by looping over some data. With Angular, it’s accomplished via the built-in ng-repeat directive. In React, nothing special is required, as we can just loop over various HTML elements and put them into an array; a benefit of using JSX.
See the Pen OPRpbR by Chris Harrington (@chrisharrington) on CodePen.
Here, we’re making use of the ng-repeat directive to add three greetings when clicking on the greet button.
Looping in React is relatively simple, as JSX is just JavaScript, so we can write a simple JavaScript loop to render what we want.
While the differences between Angular JS and React JS are large, they can both accomplish the same thing. If I appear biased in what I’ve written here, it’s because I’m biased, definitely toward React. Angular is a much fuller featured framework than React, which isn’t really a framework at all, but that doesn’t mean a lot when I don’t see the need for most of the features that Angular provides. I’ve found that I have to write less code to do more in React, and React has better performance than Angular due to React’s implementation of a virtual DOM (which I’ll prove in a future post). Despite that, support for Angular is much, much better, with a larger community and following, as React is just getting started.
Thanks for reading!
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