py4web + Svelte Demo

Demo to integrate a py4web backend with a Svelte frontend.

Requirements

• python 3.8+ with py4web
• nodejs with npm

Installation

• Python: throw this project in your py4web apps folder
• Svelte: (from the views/svelte folder) run npm install and npm run dev (for development, live builds) or npm run build (for production, manual builds)

Props/data

All data that you return in the controller, will be passed as 'props' to the frontend page. This means you can use them as js variables.

example:

if you return {'name': 'World', 'value': 15} in a controller, you can use those values like:

export let name; // this will get the value World
export let value; // this will get the value 15

Because of this feature, you always have to return a dictionary at the end of each controller. The values you return have to be JSON parsable.

Routing

Svelte is normally used for single-page applications (SPA), but there are multiple ways to use it with multiple pages:

• Making multiple files like main.js, where you instantiate the right Component for that page (lot of manual work)
• Using a routing library like svelte-routing to show a Component based on the current URL. This works best for an app without backend, but when using a backend you have to define your routes twice.
• *Providing a view variable in the backend and using that to dynamically show the right component. This is the approach I took in this demo.
  • If you want to add a new front-end page, you first have to make a Svelte page in src/pages and then import it and add it to the components object in main.js
  • You can use choose the page for a controller function with the @svelte decorator defined in models/svelte.

  @actions.uses(Svelte('Alternate'))
  def alternative_frontend():
      # this page will be using the Alternate.svelte page
      return {}

Demo pages

• /index shows that you can give information from the backend to the front-end
• /page2: demo of some Svelte features
• /non_svelte shows that you can show pages without svelte