Alex Richey

Software Engineer @ Meural

Setting Up Server Side Rendering with React, Redux, and Django

At Meural, we decided to implement server side rendering in order to increase our SEO exposure and to make social media sharing more effective. In this post, I’ll talk about how server side rendering works and the implementation that I developed.

Background

In traditional web applications, web pages are rendered on the client side. The browser receives a blob of JavaScript from the server, processes it, and paints the UI that the user sees. In server rendered applications, on the other hand, the first render of a web page is done on the server. The browser receives a pre-rendered page, which it can display without running any JavaScript. This enables better SEO exposure, since many web crawlers cannot run JavaScript, and faster perceived page load times.

There are also some downsides to server side rendering. These include slower server response time and, in lower bandwidth environments, slower time to interactive. For apps that run behind login screens, whose content is private, these downsides might make server side rendering less than worthwhile. For our use case, however, the benefits well outweigh the costs. Most of our app’s pages are public facing, so exposure to web crawlers is essential.

Preliminary Considerations

Implementing server side rendering is not a trivial task. In response to this fact, a number of libraries have emerged to make implementation a bit easier. These include Next.js, Razzle, numerous boilerplates, and others.

These libraries and frameworks can be a good choice for rapidly prototyping a feature or when starting a new app, but I would not recommend them for use in production or for extant apps. The reason for this is that using them requires surrendering a large portion of your codebase to them, which makes debugging and optimization more difficult, if not impossible, and makes you ignorant of how your app is really working. What’s more, integrating such a framework into an extant application is often more trouble than it’s worth.

Therefore, I developed a custom implementation of server side rendering at Meural. I hope that our stack is similar enough to that of other companies so that other developers might find this article useful. Our frontend uses React, React Router 3, and Redux, while our backend is a monolithic Django application.

The High-Level View

At a high level, setting up server side rendering consists in setting up the following chain of events.

SSR Schema

Since our primary application server is a Django application, which cannot understand JavaScript, we need a JavaScript runtime to render our React frontend. For this, we’ll use a Node server. When a request hits our primary Django server, we’ll query our database to get the info we need. Next we’ll send that info in an HTTP POST request to our Node server, which will return our markup, plus the final state of our Redux store. Finally, we’ll embed this information into the HTML response of our Django app and send it to the client.

Node-Django Interaction

Let’s begin by setting up the Node server. I decided to use Express.js because it is battle-tested and very easy to use.

I recommend writing a simple render and buildInitalState functions for testing purposes that simply return some valid output of any kind. I also recommend testing this server with cURL before moving on to anything else.

Now let’s wire up the Django app and test it’s interaction with the Node server.

Here’s how we insert the rendered HTML payload into our Django template.

We can now test the interaction between Node and Django. Let’s start the Node server and the Django server, open up a browser, and go to the url that corresponds to our sandwich view. To prevent our React frontend from taking over the page on load, we’ll disable JavaScript in DevTools. If you see a page with the output that you defined in your render and buildInitalState functions, then all is well.

Defining the Render Function

It will be instructive to first look at the code of the render function and then to explain how it works.

The first thing the render function does is configure the Redux store. I used the same configureStore function that I had already defined in following the usual Redux API pattern.

The second thing the render function does is get the frontend routes of my React app, by calling a function I wrote called getRoutes. This function takes the Redux store as an argument and returns all of the routes to my app. It prevents code duplication because I can call it in both server and browser environments (See the Handling the Client Side section below to see how it is used in a browser environment).

The name getRoutes, though accurate, is somewhat incomplete. The function does not just get routes. It also gets the React components of which my app is composed, since they are embedded in the definitions of the routes themselves. Therefore, the getRoutes function is what links my existing React app to the render function.

Next, in order for the render function to match the desired route, I use React Router’s match function. This function’s first argument is an object containing all of my app’s routes as its first key — which we have from the getRoutes function — and the desired route as the second key. The match function’s second argument is a callback that gets evoked after matching is complete. In a successful matching, this callback’s third argument is a renderProps object. These renderProps represent the state of my app’s props at a given route. I pass this object into React-Router’s <RouterContext> component (which is a static version of its more familiar <Router> component) to render the state of our app at the matched route.

To give the components of my app access to the Redux store, I wrap the <RouterContext> component with the <Provider> component from the React-Redux library.

Next, I call ReactDOMServer#renderToString with this wrapped component as its argument to render the state of my application at the matched route to HTML.

Finally, I call getState on my Redux store to extract its final state in case the rendering process changed anything.

If the match function fails to match the desired route, the second argument of its callback is a redirectLocation argument. In this case, I recursively call the render function with this new desired route. I am confident that there will never be a chain of infinite redirects because I have defined a wildcard route to handle such cases.

Calling the Render Function

The render function will not work as it is currently defined. The reason for this is that the JSX used in the function itself, as well as in the rest of my app, is not understood in Node runtimes. Therefore, I use Webpack and Babel to transpile my render.jsx file into Node compliant code. All I had to do to make this work was to copy my existing webpack config, change the entry point to render.jsx, and replace the target parameter with target: ‘node’.

When transpiling, I ran into some errors. Since this version of my React app will not be running in the browser, window and document will not be defined. Therefore, I had to move all references to window and document to functions that are executed only after the DOM is accessible. This involved moving references to window and document from methods like Component#constructor to methods like Component#componentDidMount. Unlike Component#constructor, Component#componentDidMount will only be called after the component has been mounted to the DOM. I also had to abandon some third-party libraries that relied on window or document in problematic places.

Handling the Client Side

Now that my server responds with a fully rendered page of my app, I need to adjust my client side JS to expect this. Here’s the code I wrote.

You might have noticed that I added an async attribute to my script tag in base.html. The async attribute makes the tag non-render-blocking, which means that the browser won’t wait for the entire script to download before rendering. This produces a considerable speed increase, especially with large JavaScript bundles. However, it also means that it is possible for the script to be executed at any time during the load process, which means that the standard procedure of waiting for DOMContentLoaded before rendering with ReactDOM might not always work, since DOMContentLoaded might have already fired, in which case, the React app would never get executed and the page would never become interactive. Therefore, I check the document.readyState when the bundle is initially executed. If the readyState is complete or interactive, I initialize my React app right away. Otherwise, I add listener for DOMContentLoaded and use my initialize function as the callback.

In my initializeApp function, I get the current state of the Redux store from the window and pass it into configureStore to setup Redux. Next, I match the current route, just as I did on the server side, using the same getRoutes and match functions which I discussed above. Instead of calling ReactDOM#render, which is the usual pattern in client rendered apps, I call ReactDOM#hydrate, which sets up React’s virtual DOM and installs listeners to make the page interactive.

Conclusion

Since deploying this project, we have seen much better SEO at Meural. Now a Google search for the terms meural and some artist’s name will yield a result of that artist’s page or one of her playlists, if that artist is in our collection. Prior to this deployment, this was not possible, since we had exposed only one webpage, which contained our single-page React app.

From Philosophy to Computer Science

image When I say that I’m a software developer with a background in academic philosophy, many people react with surprise, as if I had jumped between completely divergent fields. Philosophy and computer science are in fact closely related and it is easy to transition from one to the other. In this article I would like to highlight a few reasons why this is so, with the hopes of dispelling the common misperception that they are opposites and of giving some background for students of philosophy who are interested in transitioning to computer science.

Logical Similarities

The basis of both philosophy and computer science is logic. In philosophy, it’s often used to evaluate arguments, whereas in computer science, it is the means by which the processor is given instructions. Having a good grasp of logic’s core concepts is essential to do well in either.

Consider this example to see what I mean. Suppose I say,

If Trump or Hillary wins, then all is lost.

This statement can be represented in philosophical notation as follows:

(1) (A ∨ B) → C

where A is "Trump wins", B is "Hillary wins", C is "All is lost," and and are shorthand for "or" and "If … then …," respectively.

Now let’s write a simple program that captures the content of our claim. Let’s make our computer print "All is lost," if either Hillary or Trump win, and print "Not all is lost," if neither of them wins.

if trump_wins || hillary_wins
    print "All is lost."
else
    print "Not all is lost."
end

Cool. If we run this program after the election, it will print "All is lost," or "Not all is lost," depending on the result. Notice that, as far as the logic is concerned, we’ve used the exact same concepts that we used in expressing (1). The only difference is syntax. Here, the is represented as a multi-line command and is represented as ||. The other addition that we’ve made is to add an imperative, namely, print. This is one of the main differences between pure logic and programming: Computers do things in the physical world; pure logic does not.

The advantage of a background in philosophy is that you are already able to translate colloquial statements into logical formulae, just as programmers do. As a student of philosophy, moreover, this kind of knowledge allows you to craft and criticize arguments. As a computer programmer, the same knowledge enables you to see several ways of building the same program; and the ability to see the far reaching, logical entailments of your claims often makes it easier to spot bugs.

Analytical Similarities

The way that one evaluates a philosophical position is surprisingly similar to the way a computer processor evaluates code. Both involve analytically determining what follows from what.

Consider the position of utilitarianism. According to this view,

What is good is what maximizes happiness. The virtuous choice is the one that maximizes happiness.

In order to evaluate this position, we need to consider its implications and ask if they are sound. If there is an unsound consequence, then the following logic will undermine the position. Schematically, where ¬ is 'not,' A is "What is good is what maximizes happiness," and B is some unsound consequence, we have:

Assume:            A → B
Assume:            A
By Modus Ponens:   B
Assume:           ¬B
By Modus Tollens: ¬A ∎

This argument shows that, if there is some unsound consequence B, then A cannot be true.

In computer programming, the style of thinking involved is remarkably similar. Suppose you are writing a computer program that plays chess and you need to write a function that checks the board to see if there is a checkmate. You might start out with something like this:

def checkmate?
  if current_player.king.is_capturable?
    return true
  else
    return false
  end
end

This function checks to see if the current player's king can be captured. If it is, it returns true; otherwise, it returns false.

In order to evaluate this code, we perform a mental stack trace, that is, we imagine, as best we can, how the computer will process the code that we have just written. If our code is successful, all checkmated boards will be identified; otherwise, they won't be. Similarly, in the philosophical case, we evaluate our position by imagining all possible entailments. If our position is successful, we'll agree with all of the entailments; otherwise, we won't.

As it turns out, both of these cases are deficient. The problem with utilitarianism (at least in its current crude form) is that it ends up implying that slavery is not wrong, on the grounds that the intense suffering of the few may result in the highest levels of happiness for the many. This is unacceptable, so the argument above obtains. Analogously, the checkmate function will misidentify checked boards as being checkmated. The fact that the current player's king can be captured just means that she must move her king out of check, not that its capture is inevitable.

The point, however, is that both computer programming and philosophy involve analytically determining the consequences of one's statements; and both necessitate a certain creativity in subsequently modifying one's statements accordingly.

Historical Development

Besides these concrete similarities, academic philosophy played a fascinating role in the historical development of computing.

The conceptual work that made the advent of modern computing possible took place in the early seventeen hundreds, when the philosopher and mathematician G.W.Leibniz developed an algebraic logic. In this logic, ones and zeros represent true or false states. The reason this is significant is that Leibniz’s ones and zeros would later be rendered mechanically as on or off switches in the first primitive computers. Although it took several hundred more years and the work of countless other philosophers, mathematicians, and engineers to develop our modern notion of computing, its conceptual foundation can be traced back to Leibniz’s philosophical logic.

The influence of philosophy on computer science did not stop at Leibniz, however. In the early nineteen hundreds, the philosophers Bertrand Russell and Alfred North Whitehead wrote Principia Mathematica, a nearly 2,000 page book written largely in formal logic that aimed to couch all of mathematics in terms of logic. Although the primary aim of this book was later demonstrated to be impossible by Gödel, the Principia also set out a theory of types that was later put to use by computer scientists. According to Constable’s brief history, Russell and Whitehead’s theory of types

…provided a basis for both a precise semantics and elegant programming logics. It was in this context that computer scientists and logicians created the type theories that are deeply connected to Principia Mathematica and serve now as comprehensive logical accounts of computing, computational mathematics, and programming logics (Constable 3).

Today the influence of philosophy on computer science continues, especially in the ares of artificial intelligence, the representation of information, language, and other things.

SkiFree

Here's a clone of the classic game SkiFree that I made with Javascript Canvas as part of a/A's curriculum. Check out the repo on GitHub here. Click to begin and use the mouse to control your skier.