@saasquatch/immutable-cdn NPM

immutable-cdn

Manages a switchable CDN cookie for implementing the Immutable Web App concept of Static assets are independent of the web application environments(s).

Why?

Typically in a single page web application, you would have an index.html similar to the following:

<!DOCTYPE html>
<html>
  <head>
    <!-- Favicon, meta attributes, etc. -->
  </head>
  <body>
    <!-- Where your application renders, e.g. for React -->
    <div id="root"></div>

    <!-- Pull in your application bundles -->
    <script type="module" src="http://example.com/my-application.es.js"></script>
    <script nomodule src="http://example.com/my-application.umd.js"></script>
  </body>
</html>

In an immutable web app, you would want to server render this HTML, dynamically replacing http://example.com with the URL of your current bundles.

This has several advantages for your application bundles:

They are separated from your application environment
- The bundle can be switched out by changing a setting on your backend, which makes deploying new frontends very simple
They do not need to include any environment-specific configuration
- Your server can render this configuration directly in the HTML, e.g. in a script tag in the <head> that sets some environment-specific configuration on window which your application can pick up
- You do not need a build of your application for each of dev, staging, production and there are no environment variables baked into your bundles (e.g. like REACT_APP_*)

This is great for deployments, but in development it is also very convenient to run your frontend locally (e.g. npm run start with Create React App), and then use your local frontend directly in your deployed environments.

This package provides a simple management layer for a CDN cookie, which can be switched on the fly by changing a URL parameter and lets you specify what bundles you would like pull in from the CDN.

How to use

Once configured, you can add the cdn parameter to any URL in your frontend application to switch CDNs on the fly:

&cdn=https://some-other-cdn.com

You will be prompted to change the CDN and the cookie will be modified.

To revert to the default CDN / clear the cookie, use:

&cdn=none

Getting Started

Install the package:

npm i @saasquatch/immutable-cdn

Pull the package into your HTML from your favourite npm package CDN and initialize:

<!DOCTYPE html>
<html>
  <head>
    <!-- Favicon, meta attributes, etc. -->
    <script src="https://unpkg.com/@saasquatch/immutable-cdn@latest/dist/immutable-cdn.umd.production.min.js"></script>
  </head>
  <body>
    <!-- Initialise the CDN -->
    <script>
      window.CDN.init({
        defaultCdn: "http://example.com",
        cookieName: "CDN" // Defaults to 'CDN'
      });
    </script>

    <!-- Where your application renders, e.g. for React -->
    <div id="root"></div>

    <!-- Pull in your application bundles -->
    <script type="module" src="http://example.com/my-application.es.js"></script>
    <script nomodule src="http://example.com/my-application.umd.js"></script>
  </body>
</html>

In the server rendered HTML case, this is all you have to do - the cookie CDN will be provided to your server and it can use this to dynamically change the URL of any resources your frontend will need when it renders the HTML.

Client-specified resources

If you want to dynamically add resources to your HTML from your CDN client-side, you can specify the tags options with a list of tags and their attributes. Any string attribute containing the special identifier %cdn% will have it replaced with the actual value of your CDN cookie.

For example:

window.CDN.init({
  defaultCdn: "example.com",
  tags: [
    { tag: "link", attrs: { rel: "stylesheet", href: "%cdn%/style.css" } },
    { tag: "script", attrs: { type: "module", src: "%cdn%/my-app.es.js" } },
    { tag: "script", attrs: { nomodule: true, src: "%cdn%/my-app.umd.js" } }
  ]
});

Would append the following HTML to your body:

<link rel="stylesheet" href="http://example.com/style.css">
<script type="module" src="http://example.com/my-app.es.js"></script>
<script nomodule="true" src="http://example.com/my-app.umd.js"></script>

If you would rather append something to the <head> instead of the <body> you can use the appendTo property:

{
    tag: "link",
    appendTo: "head",
    attrs: { rel: "stylesheet", href: "%cdn%/style.css" }
}

Current CDN value

If you need to know the current value of the CDN cookie at any point, you can use:

window.CDN.get()

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