I’m learning XState. Every time I’ve used redux I find myself getting bugs because the site state becames more and more complex and I don’t handle the transitions and possible states properly.

Also, I love Svelte. Doing the stuff I like in D3js with it is always possible, but coding with a framework that allows much more complex apps.

But I didn’t find many documentation on using both, so I decided to do this post to show it.

I’ve using CodeSandbox for all the examples so the result is visible and editable by yourself if you want to.

Using XState and Svelte

The first thing to do is using the XState state instead of the regular svelte store.

I started the project copying the standard Svelte template from codesandbox, but if working locally, you could just:

npx degit sveltejs/template my-svelte-project

and install XState by running

npm install --save xstate

Start the project running

npm install
npm run dev

Now we can create one of the simplest state machine taken from the docs, that just toggles between two states:

import { Machine } from "xstate";

export const toggleMachine = Machine(
  {
    id: "toggle",
    initial: "inactive",
    states: {
      inactive: {
        on: { TOGGLE: "active" }
      },
      active: {
        on: { TOGGLE: "inactive" }
      }
    }
  }
);

As you can see, the initial state would be inactive and can be changed to active by sending the TOGGLE action. Let’s see the javascript file that does this:

<script>
  import { useMachine } from "./useMachine";
  import { toggleMachine } from "./toggleMachine";

  const { state, send } = useMachine(toggleMachine);
  function handleClick() {
    send("TOGGLE");
  }
</script>

<style>
  main {
    text-align: center;
    padding: 1em;
    max-width: 240px;
    margin: 0 auto;
  }

  h1 {
    color: #ff3e00;
    text-transform: uppercase;
    font-size: 4em;
    font-weight: 100;
  }
</style>

<main>
  <h1>Hello {$state.value}</h1>
  <button on:click={handleClick}>Toggle</button>
</main>

As all the svelte projects, every component has three parts with the javsascript, the css and the html template.

  • The useMachine will be explained later, but gives access to the current state and the function to send actions. When the state changes, the rendered component will change too. It’s as easy as this!
  • To render the value, use {$state.value}. The $ indicates that state is a store and the value has to be accessed this way.
  • handleClick sends the action when the button is pressed. ote the on:click in the button element

This is the result:

Links

XState website Accessing a readable store value in Svelte