Flask + Svelte + TS + Vite

This template should help get you started developing with Svelte and TypeScript in Vite served via Flask.

How it was prepared

Create a new project:

mkdir flasvelte

Create a new Flask project:

cd flasvelte
pip install flask
touch server.py

Then, add a minimum code to start the flask server:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def base():
    return "Hello, World!"

if __name__ == '__main__':
    app.run(debug=True)

Prepare client:

mkdir client
cd client
npm init vite
# select Svelte then finish it

Let Flask serve the static files of Svelte:

from flask import Flask, send_from_directory
import random

app = Flask(__name__)

@app.route('/')
def base():
    return send_from_directory('client/dist/', 'index.html')

# Path for all the static files (compiled JS/CSS, etc.)
@app.route('/<path:path>')
def static_proxy(path):
    return send_from_directory('client/dist/', path)

@app.route('/random')
def random_number():
    return str(random.randint(1, 100))

if __name__ == '__main__':
    app.run(debug=True)

Recommended IDE Setup

VS Code + Svelte.

Technical considerations

Why not using SvelteKit?

• It brings its own routing solution which might not be preferable for some users.
• It is first and foremost a framework that just happens to use Vite under the hood, not a Vite app.

This template contains as little as possible to get started with Vite + TypeScript + Svelte, while taking into account the developer experience with regards to HMR and intellisense. It demonstrates capabilities on par with the other create-vite templates and is a good starting point for beginners dipping their toes into a Vite + Svelte project.

Should you later need the extended capabilities and extensibility provided by SvelteKit, the template has been structured similarly to SvelteKit so that it is easy to migrate.

Why global.d.ts instead of compilerOptions.types inside jsconfig.json or tsconfig.json?

Setting compilerOptions.types shuts out all other types not explicitly listed in the configuration. Using triple-slash references keeps the default TypeScript setting of accepting type information from the entire workspace, while also adding svelte and vite/client type information.

Why include .vscode/extensions.json?

Other templates indirectly recommend extensions via the README, but this file allows VS Code to prompt the user to install the recommended extension upon opening the project.

Why enable allowJs in the TS template?

While allowJs: false would indeed prevent the use of .js files in the project, it does not prevent the use of JavaScript syntax in .svelte files. In addition, it would force checkJs: false, bringing the worst of both worlds: not being able to guarantee the entire codebase is TypeScript, and also having worse typechecking for the existing JavaScript. In addition, there are valid use cases in which a mixed codebase may be relevant.

Why is HMR not preserving my local component state?

HMR state preservation comes with a number of gotchas! It has been disabled by default in both svelte-hmr and @sveltejs/vite-plugin-svelte due to its often surprising behavior. You can read the details here.

If you have state that's important to retain within a component, consider creating an external store which would not be replaced by HMR.

// store.ts
// An extremely simple external store
import { writable } from 'svelte/store'
export default writable(0)