Introduction

A few upsides come with adopting an opinionated framework like Ruby on Rails. One of them is having a clear pattern to the layout of a project’s source code directories and guidance on where specific code should live. This reduces the friction of creating new code modules and provides guideposts for navigating the code base. Human brains like patterns, and organizing your code into clear patterns helps developers find their way; both the newly onboarding devs and the grizzled veteran devs.

Opinionated direction is something we severely lack in many aspects of React projects, and directory layout is definitely one. Tools like Create React App have done a great job at scaffolding a working React project with a few top-level files, configs, and folders with a functional build pipeline, linting toolchain, and test harness already configured. But CRA gives you a src/ directory for all your application code with no guidance on how the files inside should be organized.

Once you’re inside a src/ folder of a React project, it’s the wild west. This often works against projects and teams. Unless they have already done a few React projects and cut themselves on all the sharp corners, it’s easy to stumble into traps and pitfalls that actively work against good React behaviors. Refactoring code becomes scary, exposed implementation details cause unnecessary tight coupling, and the pain gets worse as your project grows.

But all is not lost!

How to lay out your React project src/ folder?

“You have brains in your head. You have feet in your shoes. You can steer yourself any direction you choose. You’re on your own. And you know what you know. And YOU are the one who’ll decide where to go…”

― Dr. Seuss, Oh, the Places You’ll Go!

Let’s lay some foundational principles that are conducive to refactoring, hide implementation details, and grow with your project.

  1. Implementation code should always live in meaningfully named files.
  2. A particular piece of code should have a short list of good potential locations to live.
  3. Implementation details should be hidden behind a module interface to make refactoring easier.
  4. The location of a module or file provides hints on how and where that code is intended to be used.
  5. The layers of the application and their dependencies between each other should be apparent by the layout.
  6. The directory layout should provide meaningful guidance regardless of size: whether 30 files or 3000 files.
  7. The directory layout should reward you for good React behaviors: e.g. extracting many small components to meaningful places, extracting non-UI code out of React all together.

With those principles in hand, let’s look at an example of a project layout following these principles. This super useful and flexible React project layout has been used with great success at many clients:

.
├── build/                               #
├── docs/                                #
├── src/                                 #
   ├── lib/                             # 'lib/' is Non-UI Code
      ├── __tests__/                   # Tests in `__tests__/` dirs
         └──  ...                     #
      ├── core/                        # 'core/' is bedrock domain code
         ├── __tests__/               #
            ├──  invoices.test.js    #
            ├──  tasks.test.js       #
            └──  ...                 #
         ├── index.js                 #
         ├── invoices.js              # Pure functions of business logic
         ├── tasks.js                 # for 'invoices' domain 'tasks' domain.
         └── (otherDomains).js        #
      ├── ...                          # Other infrastructural code that isn't
      ├── httpClient.js                # tied to our domain.
      ├── moneyFormatter.js            #
      ├── dateFormatter.js             #
      ├── websocketHandler.js          #
      └── ...                          #
   ├── pages/                           # Entrypoint components for routes.
      ├── auth/                        # Each dir could map to a URL prefix.
         ├── index.js                 # (If Next.js, follow Next.js rules)
         ├── Login.js                 #
         ├── ForgotPassword.js        #
         └── Logout.js                #
      ├── invoices/                    #
         ├── index.js                 #
         ├── InvoiceDetails.js        #
         └── InvoiceList.js           #
      └── dashboard/                   #
          └── ...                      #
   ├── ui/                              # React components, contexts, and hooks
      ├── login/                       # grouped by domain or category.
         ├── __tests__/               #
            ├──  LoginForm.test.js   #
            └──  ...                 #
         ├── index.js                 # <- Only public exports for this module
         ├── LoginForm.js             # <- Login related Component
         ├── useAuthStatus.js         # <- Login related hook
         └── AuthProvider.js          # <- Login related context provider
      ├── forms/                       #
         ├── __tests__/               #
         ├── index.js                 #
         ├── TextInput.js             # <- A lone component
         ├── button/                  #
            ├── index.js             #
            ├── some_helper.js       #
            ├── InnerButton.js       # <- Private, non-exported component
            └── FancyButton.js       # <- Primary implementation of component
         ├── checkbox/                #
            └── ...                  #
         └── select/                  #
             └── ...                  #
      └── avatars/                     #
          └── ...                      #
   ├── ...                              #
   ├── App.js                           # <- Compose your top-level routes.
   └── index.js                         # <- (a) render `App` with global providers
├── LICENSE                              #    (b) mount React tree to the DOM.
└── README.md

Here are some callouts to discuss:

  1. Nesting modules
  2. lib/
  3. pages/ vs. ui/
  4. Dependencies

Nesting Modules

Notice this layout is more deep than wide, more nested than flat. This is by design. By nesting modules the developer can indicate dependency relationships between code. For instance, components that are only meant to be consumed by a specific higher-level component are nested within that higher-level component’s folder. For example:

└── src/
    └── ui/
        └── forms/
            ├── button/
            │   ├── index.js
            │   └── Button.js
            ├── checkbox/
            │   ├── index.js               # Only exports 'Checkbox' component
            │   ├── SimpleCheckbox.js      # Imports 'CheckSelectOverlay'
            │   ├── FancyCheckbox.js       # Imports 'CheckSelectOverlay'
            │   └── CheckSelectOverlay.js  # Only relevant to checkbox components
            └── select/
                └── ...

The forms/ module is composed individually of button/, checkbox/, select/, and potentially many more “forms” related modules exporting their own components. Those sub-modules can judiciously decide which code from which modules to expose via the index.js file, but they could also have deeping nesting inside of them if it makes sense.

The “lib/” Folder

The lib/ folder is the place to collect your non-UI code. The kind of code and operations that could/should survive completely changing your JavaScript framework. The lib/core/ folder is a personal favorite, as that is the place to collect your domain objects and business logic, usually in the form of pure functions. The wider lib/ folder should contain infrastructural code like network layer clients, formatting utilities, platform communication like Browser Storage or IndexDB, etc.

It is appropriate to further subdivide lib/ into useful modules as it grows. For instance:

src/
└── lib/
    ├── core/
    │   ├── index.js
    │   ├── invoices.js
    │   └── tasks.js
    ├── network/
    │   ├── index.js
    │   ├── httpClient.js
    │   └── websocketHandler.js
    ├── storage/
    │   ├── index.js
    │   ├── webIndexDB.js
    │   └── localStorage.js
    ├── formatters/
    │   ├── index.js
    │   ├── dateFormatter.js
    │   └── moneyFormatter.js
    ├── testUtils/
    │   ├── index.js
    │   └── dataFactories.js
    └── ...

At the start of a project, I recommend beginning with only lib/ and lib/core/, and to let the remaining folders emerge organically.

“pages/” vs. “ui/”

The split between src/pages/ and src/ui/ is also purposeful and by design. While ui/ is meant to be a collection of reusable React code(i.e. components, hooks, and contexts ), pages/ specifically (a) maps components to routes and (b) composes ui/ and lib/ code together. Generally speaking, code should never depend upon (i.e. import) code from pages/ except for (a) src/App.js setting up the top-level routes and (b) parent pages on sub-pages (i.e. component for route http://example.org/invoices imports component page handing route http://example.org/invoices/:id.).

Dependencies: Made More Explicit

By knowing the location of code, you should have an idea on what code is most likely to depend, or not depend, on it. In this layout, the following rules are expected to hold:

  • Code from lib/ never imports code from ui/ or pages/.
  • Code from pages/ should import implementation code from ui/ or lib/.
  • Code from ui/ may import code from lib/ but never from pages/.
  • Generally, code may import from within their own top-level namespace: i.e. pages/, lib/, ui/.

Conclusion

This React project layout prioritizes patterns that are conducive to refactoring, hide implementation details, and grow with your project. This pattern works for (a) Create React App projects, (b) Next.js projects, (c) React Native projects, and … even non-React projects. GASP! As more and more frameworks get on the “component” bandwagon, they hit the same code organization growing pains. This layout can be easily modified to work for Vue, Angular, and vanilla Web Components as well. It even supports very nicely JavaScript alternatives like TypeScript and Flow: it’s easy to put shared interfaces in meaningful locations and the dependency rules still work.

This explanation of the super useful and flexible React Project Layout is good 80%-rule guidance: 80% of the time it works every time. It doesn’t clearly explain more niche or esoteric cases, but hopefully it gives you enough of a starting point that you can make those decisions with confidence.

So give it a shot, and let me know what you think. Reach me at @tgroshon on Twitter.

Tommy Groshong

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