These are the docs for the latest stable release of the Bolt Design System. Looking for the previous release, v2.26.1?

Server Side Rendering (SSR)


This brand new SSR package currently provides three different interfaces to pre-render web components:

Option 1. via the CLI (super helpful for testing).

This Node.js CLI currently accepts two arguments: 1. The string of HTML to pre-render 2. Boolean to conditionally enable/disable syntax highlighting (which defaults to true when using the CLI directly, false when being used for PHP rendering)

$ node packages/servers/ssr-server/cli.js '<bolt-button color="secondary">SSR Test</bolt-button>'

This returns back the pre-rendered, hydration-friendly markup (with or without syntax highlighting)


Option 2. via Twig filter / function

There’s also two ways to use this SSR functionality in Twig via the new bolt_ssr Twig filter and bolt_ssr Twig function.

Both of these also use the Node.js CLI interface under the hood with the added bonus of returning back the original pre-rendered HTML as a fallback.

{% filter bolt_ssr %}
  <bolt-button color=“secondary”>
    SSR Test
{% endfilter %}

Option 3. via JS using the SSR library itself (experimental)

This SSR functionality can even be used in other JS files via the renderToString method on the @bolt/ssr-server package.

Note: currently this method currently requires the developer to manually call the shutDownSSRServer method afterwards — hopefully something we can automate in the next iteration.

Misc Notes

  • The first couple of implementations of this were powered by a Google Puppeteer instance however this latest iteration managed to swap out Puppeteer for a lighter weight JSDOM implementation that’s been lightly polyfilled! 🎉
  • SSR compile times are averaging around 1 to 1.3 seconds (when no Webpack build is required). Quick enough for a larger POC but not quick enough to globally roll this out without expensive compile times on the server

Gotchas / Next Steps

  • Auto-wire Components Waiting To Load: we should figure out how we want to create a list of the custom element tags that need to be defined before the SSR logic kicks off:
  • Cache Busting: Further work needed to get cache busting added to the SSR build process
  • Async Rendering: Look into parallelizing / making requests more async
  • Alt Interface for PHP Integtation? We should look into using web sockets or even using a vanilla server request / response interface.
  • Caching: making the same request to the same component with the same data on the same version of Bolt should pull straight from memory to speed up build times.
  • Compare SSR Perf: Further research into performance optimizations -- including doing a benchmark between say, SSR for a Vue.js component compared to our current implementation
  • Test CKEditor Integration: Test integrating CKEditor example content with this new SSR functionality
  • Combine Webpack Builds? Look into (potentially) combining the client-side vs server-side webpack builds to eliminate having to compile some of the same components twice
  • Research Further Optimizing Client-side Perf: Lighter weight JS load in the client = faster SSR response times
  • Combine Multiple Servers: Out of simplicity, we currently have 3 different Express servers -- the default Express server, the testing server when running Jest tests, and now this new SSR server. At a minimum I could see two of these getting merged together into a single server instance (if not merging together all three)
  • Handle Pre-rendered HTML: the current implementation doesn't know if the markup provided (or pieces of the markup provided) has been pre-rendered which could lead to unintended rendering quirks and/or extra unnecessary processing
  • Fragment Cache? If a button component was being pre-rendered but contained an already pre-rendered icon component, how might we handle that?

Performance Impact


  1. This is based on the current implementation which will reuses the bolt-global.server.js if a Webpack build had already been done -- this speeds up the initial SSR request.
  2. CLI benchmarks were are based on this bolt-global.server.js file already existing
  3. The current implementation is synchronous -- only one request at a time and PHP waits for the request to complete before continuing.

CLI Performance (per compile):

  • Without formatting HTML or syntax highlighting: 1.08s average (or 0.05s faster on average than with Prettier formatting)
  • With highlighting + prettier: 1.23s average
  • Without syntax highlighting, with HTML formatting: 1.13s average

Pattern Lab Compile Times (Prod) with SSR enabled (Select Usage)

  • Using it in a handful of places (~7 places): ~21.97s total compile time
  • Without SSR enabled: ~13.s total compile time

Global Usage (Tests SSR <bolt-button> Globally)

  • Pre-rendering all <bolt-button> components in the static site generator: ~1 minute, 40s compile time (vs 4s compile time normally)
  • Pre-rendering all <bolt-button> components in Pattern Lab: 11 minutes, 27.7s minutes (vs 13.2s normally)