Quotes
Display awesome quotes with style! Visit the demo here.
A little experiment
This simple project helped me to understand the basics of React and how Rails 5.1 works with Yarn and Webpack. I built this application following this awesome article, and I've made some small refactorings on the main React component.
How it works
Backend
In our Rails app we have a pages controller with a home action, which is set as root. The correspondent view renders a <div class="quotes"> which will be hooked from the javascript and filled with some great quotes.
For keeping our data we have a Quote model with the text and author fields. The model provides the next_id and previous_id methods, in addition to the "field methods" made available by ActiveRecord.
We are exposing a very simple API through the QuotesController , which is namespaced under /api. The controller provides the show REST action, so we're able to make GET requests to (e.g). /api/quotes/22. And yes, the "RESTfullness" of ActionPack is adorable.
To return a JSON representation of a quote we use jbuilder (a gem that's included by default in Rails) for the show view, and in the routes config we set json as default format, so we don't need to specify .json on the GET requests.
Frontend
When Webpack is installed and configured to your Rails app, we're able to build javascript packs and drop them into a html view, in the same way we insert an image asset (the webpacker gem makes this magic happen).
Every file in app/javascript/packs/ will be compiled into a standalone pack: in our case we will find the build of app/javascript/packs/quotes.js at (e.g.) /packs/quotes-0123abc.js (0123abc is a made-up content hash - more on fingerprinting here).
In production the javascript_pack_tag helper that we used in the pages#home view will refer to the compiled pack /packs/quotes-0123abc.js, while in development mode it will be served by the Webpack dev server, which does some magic tricks, like hot reloading. That's why is handy to run foreman (foreman start -f Procfile -p 3000), instead of manually starting Puma and the Webpack server.
(if we go to the source page when in development mode, and we peak in the js file, we will get presented a huge file: that is webpack that is giving us the magic - in production we will get a reasonable-sized compiled file).
React components
quotes.js imports the React and ReactDOM modules from node_modules (which are installed by Yarn when the webpacker:install task is run), as well as the App component from the components folder (we don't need to specify the .jsx extension).
App
The Router is the main part of our project. It renders React components depending on the current URL in our browser.
App is basically a wrapper for Router: it just passes firstQuoteId to it, so techically is the root of our application. It's rendered by ReactDOM in our page, inside <div class="quotes"> that we can find in home.html.erb.
Props
React components can render other components, passing them some arguments called props. A prop is an object property that is shared between a parent component and a child, and the changes on the parent propagate down to the child (that can in turn can share it with some of its children).
Basically, props are just read-only piece of data sent to a component by its parent: most of the components in our applications should simply read props that they receive, and render them.
In our case we need to to pass the id of the first quote in our database, from the Rails backend to the Frontend: instead of passing it trough the API, it's convenient to pass it through the data attribute of the<div class="quotes">. We store it on the constant firstQuoteId, then, when the ReactDOM renders the App component, it passes the firstQuoteId prop to it.
Router
The Router, in addition to keep an eye on the browser address, renders a Route, which renders the QuoteDisplayer component. The Route passes to the QuoteDisplayer all its props (thanks to {...routeProps}), plus the firstQuoteId prop, made accessible by App.
QuotesDisplayer
This component is rendered by App. More specifically: it's rendered by the Route that is rendered by the Router. The Router is exported as App , imported in quotes.js and rendered by ReactDOM.
This object extends the "React Component" object, and its state is initialized with an empty quote property.
Before QuotesDisplayer is mounted on the DOM, it runs its constructor method and componentWillMount, which calls setQuoteIdFromQueryString() and setQuote().
After running componentWillMount the component is rendered on the DOM (the first time it renders nothing because this.state.quote has not been set yet).
setQuoteIdFromQueryString parses the query string and stores the id of the quote on its quoteId property (it gets the query string from the search property of the location prop, which is passed by the Route object)
setQuote, thanks to the axios library, makes a GET request referencing the quote id we set before. When the promise will be resolved, setState() will store the quote object described on the JSON on the quote property of the component state - which is readable through this.state.quote.
After running componentWillMount() the component will render, but since the promise has not been fulfilled, the quote property in our state is still an empty object, and the first time we render the component we will just render an empty template.
When we receive the response from the Rails server we set the state of our component with this.setState, and every time the state of the component mutates, it is re-rendered. Since this time this.state.quote has been set, we're able to correctly display the content of our quote. Yay!!!
Link and Route
When we click on the "next" link, the Route detects a new location, and since it sends the location prop to QuotesDisplayer, this said component should be re-rendered. When it receives a prop, (and before re-rendering) it will run componentWillReceiveProps(), which sets the new quote id with setQuoteIdFromQueryString, and runs setQuote to make another GET request and set a new quote object in our state.
Updating with props and state changes
React components will re-render every time they receives a new prop or when their internal state mutates. In our case we want QuoteDisplayer to update the DOM only when its state mutates after we receive the JSON object, and not when it receives the location prop from the Route.
To avoid extra renderings we can override the shouldComponentUpdate method, which lets us compare the new state we are getting with the current state we are in. The shouldComponentUpdate is not invoked when the component is mounted and appears for the fist time on the DOM.
Considerations
For this specific project it would be probably better to have a JSON response with an array with all the quotes, but I think that's a good example to work with multiple XHR calls. Actually, it would be interesting to integrate Redux to experiment with time travelling!