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Vite with Flask Backend

This repository is a minimal but complete proof-of-concept for a Vite backend integration with Flask. It is loosely inspired by Laravel's asset bundling, but provides a much lighter abstraction between Vite and the Flask backend. The techniques used in this project could be adapted to integrate Vite with other backends like Go, Django, Ruby, and others.

This demo supports TypeScript and Scss, but other file formats like JSX could be added.

Note

I wrote an in-depth blog post about this integration–check it out if you want to learn more about how this repo works!

How to use Vite assets in this demo

To add an input asset (equivalent to a Webpack entrypoint), first add it to the build.rollupOptions.input array in vite.config.js. The asset must live in the assets_source/ directory.

// Truncated vite.config.js file

export default defineConfig({
  build: {
    rollupOptions: {
      input: ["assets_source/scripts/app.ts"],
    },
  },
  // more configuration...
});

To use the asset in Flask, use the asset() helper in the Jinja2 html templates, passing it the path of the asset within the assets_source/ directory.

<script type="module" src="{{ asset('scripts/app.ts') }}"></script>

Any assets imported by app.ts will automatically be included by Vite.

Setting up the local development environment

Install the npm dependencies.

npm install

Create a Python virtual environment then install the Pip dependencies.

python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Running the app in development mode

In one terminal window, start Vite in development mode.

npm run dev

In another terminal, start Flask in debug mode, which provides automatic app reloading while developing.

flask --debug --app main run --port 8000

For more Flask CLI arguments, check this post.

Running with production assets

First, build the production assets:

npm run build

Then boot the production server with the following command:

gunicorn --workers 4 --bind 127.0.0.1:8000 'main:app'

Potential gotchas

Assets may be accidentally omitted in production

Vite's development server will build & serve all requested files within the assets_source/ directory, even if they are not included in the build.rollupOptions.input array in vite.config.js. If input files are not included as input assets in Vite's config file, they won't get built when running npm run build, and therefore won't be available in production.

Ensure that any asset that is referenced in a template is also included in Vite's input asset array in prior to building the production assets.

The JS entrypoints don't need a modulepreload polyfill

Vite's Backend Integration Guide mentions adding import 'vite/modulepreload-polyfill' to the top of JS entrypoints if build.polyfillModulePreload is not disabled. Vite automatically generates directives for entry chunks and their direct imports in the built HTML (docs), but Vite is not building our HTML templates, and our Jinja templates don't implement module preload links.