Here at SparkPost we have a “single-page JavaScript app” that consists of about 50,000 lines of early 2015-era Angular 1.x code spread across more than 400 files. It’s not a small app. And as you’d expect with almost any language or framework over a period of 2 years, we’ve gotten pretty familiar with Angular’s good, bad and ugly sides. Angular 2, having been released as “Final” in September of last year, would seem like a pretty natural fit for us. But the title of this post has already given it away: we’re most likely not upgrading to Angular 2.

Why not Angular 2? Mostly because of a migration path that makes a strong case for considering almost anything else and maybe somewhat because of TypeScript, but if I’m being honest it’s mostly because it’s nice to try new things. We’re not an agency with a new greenfield project kicking off every few weeks or months where we can test out the latest pre-alpha releases of our favorite cleverly-named JavaScript libraries. Fifty thousand lines of code changes slowly. But that’s when the “tools app” showed up.

A rare greenfield project

Our team was asked to build a set of email tools that wouldn’t live inside of our existing app. These “hardcore email tools” help developers with deep cut email setup—the kind of stuff we already take care of for SparkPost customers —so we wanted them to have their own space out from behind our login. Suddenly, we had a place to explore something new [cue harp music].

We came up with some important criteria for what we’d use to build this new app:

  • It needed to be easy to learn
  • It needed to be fast to build
  • It needed to be something we could build in the open
  • It needed to not be Angular
  • It needed to probably just be React

After considering these criteria carefully and thoughtfully as a team, we came to a surprising decision to give React a try. At the time, I was the leading React expert on our team by way of having completed one Udemy course on the subject, so I began to throw something together.

Some things we accidentally did right

We already had a small part of the app designed and built. It’s hard to underestimate the value of a designed, styled, and approved working prototype of even just a small part of your app. The time that could have been spent arguing over button placement and wording was replaced with figuring out how to get a React app off the ground.

Speaking of which, we used Create React App. Think “html5boilerplate for React apps,” or maybe “Ember for React apps.” CRA gives you a working React starting point complete with all the dependencies (literally, it might download all of the dependencies) and with a working baseline Webpack configuration. Again, this let us focus on what we were actually building. And when you’re ready, CRA lets you “eject” and take control of the whole setup. It’s fantastic and you should use it.

You should also find a designer who can do both. And by both I mean design and understand React. I know this is a very unfair thing to suggest because it really seems to be incredibly hard to find, but we found one of these magical unicorns and they’ve been invaluable. (I even looked up “invaluable” just now to confirm that it does mean really freaking valuable.) If you can, make it a priority to hire this kind of person for your team. (And thanks for being awesome, Jon.)

We also made a decision early on to build the app using only setState / local state, i.e. no Flux, no Redux, etc. We eventually added Redux—another topic for another time—but starting with a simple React app made it much easier to onboard new developers who were getting up to speed with a lot of things at once. Not to mention, waiting on Flux also lets you decide if you really need it at all.

A few other things I’d recommend based on our first-timer experience:

  • Use Jest for your testing. Jest comes with Create React App and despite being 100% Mocha/Chai across all of our other projects, it was too hard for us to deny how great Jest is. Notably, the amazing Jest CLI and Snapshot testing have both been especially useful additions for us.
  • Use the dev tools. There are ones for React (Chrome, Firefox) and ones specifically for Redux if you use it. They’re free, they work great, and they’re incredibly useful.
  • Find a group of people you trust, ask them for advice, and do what they say. I’m fortunate to have friends in our local meetup group (CharmCityJs) and in the NYC JavaScript community (BoroJS), both with active Slack teams. Being able to ask “what do people use for x?” has been a huge help because really, you just need to pick something. Trusting someone else is as good a reason as any.

Fifty thousand lines of code changes slowly

So what about that 50,000-line Angular app? We won’t be migrating it to React, at least not directly, and it can’t really survive as an Angular 1.x app forever, either. But here’s an interesting thing I noticed as I was getting familiar with React: in some ways, it’s not that much different than Angular. Here’s an Angular 1.5+ component:

const template = `<div>
  <h1>{{ banner.message }}</h1>
  <button ng-click="banner.update()">Update message</button>

class BannerCtrl {
  constructor() {
    this.message = 'Some default message'

  update() {
    this.message = 'New message'

export default angular.module('bannerComponent', [])
  .component('banner', {
    controller: BannerCtrl,
    controllerAs: 'banner'

If you pretend the template string is some JSX and it gets returned from that controller’s render method, you basically have a React component (at least structurally). So instead of trying to haul 400 files’ worth of old-school, big-controller Angular code into a new framework, our plan is to focus on the patterns. Specifically, the patterns of “small, focused components” and “unidirectional data-flow”. I’ll talk more about that second part in a later post about our adventures with Redux, but refactoring our giant controllers into small Angular components has two big advantages:

  1. React isn’t forever. Any large-app rewrite/refactor is going to take a while, and if you haven’t noticed, the JavaScript ecosystem moves pretty quickly. By focusing on refactoring our existing app to use better patterns, we get it prepared to migrate to whatever happens to be the best solution at the time, when we’re finally in better shape to make that move.
  2. Iterative, incremental development is dangerous. One of my favorite images of how “agile development” should work is a drawing by Henrik Kniberg from a Spotify presentation, explaining how to be iterative in a productive way. You’ve probably seen it before:
react agile illustration

If we spend 6 to 9 months or more trying to rewrite the app in React and don’t succeed, run out of time, or have the work shelved for other priorities, we end up with nothing useful at all. But with the refactor-first plan, the worst thing we end up with is a better, more maintainable Angular app. In other words, it’s an easy decision.

Angular, React, Kumbaya

No lie, we had a lot of fun building our new tools app in React/Redux. It’s a great library with a fantastic ecosystem and a lot of good patterns. But to be honest, our Angular app already works, and that’s fine. If you’re maintaining a big legacy app, remember:

  • Find small greenfield projects where you can build something with new tools.
  • Focus on patterns, and figure out how you can incorporate those patterns into your legacy app without having to rewrite the whole thing.

As I mentioned before, we built this in the open, so feel free to check out the code as well as the live app itself. If you’re coming from an Angular app, I’ve written up a bunch of notes about learning React that may be helpful for you, too. If this post was interesting to you for any reason at all, check back often as we continue to write more about our adventures with Angular, React, and front-end development. If you have any questions or if there’s anything else specific you’d like to hear about, let us know!

–Jason Rhodes