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README.md

react-immutable-example

This project demonstrates how to convert to an Immutable Web App from a React app that was generated with Create React App version .

Getting Started

This project was created by running:

> npx create-react-app react-immutable-example

> cd react-immutable-example

Immutable Conversion

Converting this this new application to build an Immutable Web App requires the following steps:

  1. Referencing environment variables defined on window
  2. Rendering an index.html template for deployments
  3. Running locally

Referencing environment variables defined on window

Create React App has documentation for adding custome environment variables. As they mention in the documentation, the environment variables are embedded during the build-time. To make the assets immutable, the setting of values must be shifted from build-time to run-time. Create React App has documentation for injecting data from the server into the page which is similar to how this Immutable Web App example will handle environment variables.

Change all references to point to the run-time browser window object instead of the build-time node process object:

- process.env.REACT_APP_VARIABLE
+ window.env.REACT_APP_VARIABLE

Rendering an index.html template for deployments

In theory, the role of index.html in an Immutable Web App is to be a deployment manifest that only contains configuration that is unique to the environment where it is deployed.

In practice, there is often a need to include markup or scripts in the index.html that are more than just configuration, or that doesn't vary by environment, or that does change between versions of the app. This issue can be resolved by creating an immutable index.html template, that is published with the other immutable assets.

Converting index.html to a template

This example uses EJS as the templating language to render index.html, but any templating language can be used.

  1. Identify the parts of the index.html that vary by environment:

    • PUBLIC_URL: URL where the versioned immutable assets will be deployed.
    • window.env: Environment-specific JavaScript configuration.
  2. Set PUBLIC_URL to an EJS template string in the .env:

+ PUBLIC_URL=<%=PUBLIC_URL%>
  1. Set REACT_APP_ENV to an EJS template string in the .env. This will contain the JavaScript environment-specific variables.:
  PUBLIC_URL=<%=PUBLIC_URL%>
+ REACT_APP_ENV=<%-JSON.stringify(env)%>
  1. Add a new script tag to render the JavaScript environment-specific variables in public/index.html:
<head>
    ...
+   <script>
+       env = %REACT_APP_ENV%;
+   </script>
</head>

Example

public/index.html:

The source template that is converted into an immutable template during the build.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <meta name="theme-color" content="#000000">
    <link rel="manifest" href="%PUBLIC_URL%/manifest.json">
    <title>React App</title>
    <script>
      env = %REACT_APP_ENV%;
    </script>
  </head>
  <body>
    <noscript>
      You need to enable JavaScript to run this app.
    </noscript>
    <div id="root"></div>
  </body>
</html>

.env

The build-time environment variables used to generate the immutable template.

PUBLIC_URL=<%=PUBLIC_URL%>
REACT_APP_ENV=<%-JSON.stringify(env)%>

dist/ng-immutable-example/index.ejs

The immutable template that is published along with the other versioned, immutable assets. It is combined with config.json to render the index.html that is a deployment manifest.

<!doctype html>
<html lang="en">
  <head>
      <meta charset="utf-8">
      <link rel="shortcut icon" href="<%=PUBLIC_URL%>/favicon.ico">
      <meta name="viewport" content="width=device-width,initial-scale=1,shrink-to-fit=no">
      <meta name="theme-color" content="#000000">
      <link rel="manifest" href="<%=PUBLIC_URL%>/manifest.json">
      <title>React App</title>
      <script>env = <%-JSON.stringify(env)%>;</script>
      <link href="<%=PUBLIC_URL%>/static/css/main.6bd13355.chunk.css" rel="stylesheet">
  </head>
  <body>
      <noscript>
        You need to enable JavaScript to run this app.
      </noscript>
      <div id="root"></div>
      <script>...</script>
      <script src="<%=PUBLIC_URL%>/static/js/1.a700ff87.chunk.js"></script>
      <script src="<%=PUBLIC_URL%>/static/js/main.b75225a8.chunk.js"></script>
  </body>
</html>

config.json:

The environments-specific values that vary. This is combined with the published immutable template to be rendered into index.html. It is not an immutable asset and should be managed as deployment-specific configuration.

{
    "PUBLIC_URL": "https://assets.react-immutable-example.com/1.0.0",
    "env": {
        "api": "https://api.react-immutable-example.com"
    }
}

Rendered index.html

The environment-specific deployment manifest. It is the product of rendering an immutable template against the config.json. Publishing this file to the web application environment is an atomic deployment.

<!doctype html>
<html lang="en">
  <head>
      <meta charset="utf-8">
      <link rel="shortcut icon" href="https://assets.react-immutable-example.com/1.0.0/favicon.ico">
      <meta name="viewport" content="width=device-width,initial-scale=1,shrink-to-fit=no">
      <meta name="theme-color" content="#000000">
      <link rel="manifest" href="https://assets.react-immutable-example.com/1.0.0/manifest.json">
      <title>React App</title>
      <script>env = { api: "https://api.react-immutable-example.com" };</script>
      <link href="https://assets.react-immutable-example.com/1.0.0/static/css/main.6bd13355.chunk.css" rel="stylesheet">
  </head>
  <body>
      <noscript>
        You need to enable JavaScript to run this app.
      </noscript>
      <div id="root"></div>
      <script>...</script>
      <script src="https://assets.react-immutable-example.com/1.0.0/static/js/1.a700ff87.chunk.js"></script>
      <script src="https://assets.react-immutable-example.com/1.0.0/static/js/main.b75225a8.chunk.js"></script>
  </body>
</html>

Running Locally

Without making any additional changes, npm start will run and serve the static assets as well as attempt to serve the immutable template index.html. A proper index.html can be rendered by overriding the .env file with values instead of template strings in an .env.local file.

.env:

PUBLIC_URL=<%=PUBLIC_URL%>
REACT_APP_ENV=<%-JSON.stringify(env)%>

.env.local:

PUBLIC_URL=/
REACT_APP_ENV={ api: "https://localhost:3001/api" }

Future Work

This project will be updated as better patterns for building Immutable Web Apps are established and as Create React App changes.