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style_loader_vs_mini_css.md

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CSS Delivery In Development

You have two options for serving CSS in development:

  1. You can opt to serve CSS via style-loader (as was traditionally done in a Webpack setup), where CSS is written by Javascript served by Shakapacker into a <style> tag, or
  2. You can opt to serve CSS as a full CSS file via mini-css-extract-plugin, which uses a standard <link> tag to load a fully separate CSS file.

Both options support HMR. The default is style-loader. If you want to use mini-css-extract-plugin in development, set inline_css: false in the development dev_server section of your shakapacker.yml:

development:
  <<: *default
  dev_server:
    hmr: true
    inline_css: false # Use mini-css-extract-plugin for CSS delivery

Why would I pick style-loader?

style-loader is how you are probably are used to serving CSS in development with HMR in Webpack.

benefits

drawbacks

  • Inflated JS deliverable size; requires JS execution before CSS is available
  • FOUC on initial page load
  • Adds an extra dependency
  • Divergence in delivery mechanism from production

Why would I pick mini-css-extract-plugin?

mini-css-extract-plugin's behavior is much more true to a production deployment's behavior, in that CSS is loaded via link rel=stylsheet tags, rather than injected by Javascript into style tags.

benefits

  • Required for production, so it's going to be in play anyhow. Using only it simplifies the config and eliminates the style-loader dependency.
  • No FOUC on initial page loads
  • CSS delivered via <link> tags matches the mechanism used in production (I have been guilty of omitting my stylesheet_pack_tag for my first deploy because CSS worked fine with just the javascript_pack_tag in development.)

drawbacks

  • Invokes a separate HTTP request, compared to style-loader
  • Potential for FOUC on HMR refreshes
  • More data transferred per refresh (full stylesheet reload, rather than just an incremental patch). Not likely to be noticed for local development, but still a technical difference. This may only be the case when you're using local CSS modules.