svelte-websocket-stores

Synchronize primitive-typed Svelte stores across a simple WebSocket connection.

Purpose

This was originally designed to allow touch panels to use Svelte with any backend.

Usage

Initialization main.ts

import { WebSocketWrapper } from "svelte-websocket-stores"

export const sws: WebSocketWrapper = new WebSocketWrapper("ws://192.168.0.64:80", "tp1");
sws.start();

Write-only example component.svelte

<script>
    import { sws } from "main.ts";

    let pressStore = sws.webSocketStore<boolean>("myCoolButton.press");

    function press() {
        $pressStore = true;
    }

    function release() {
        $pressStore = false;
    }
</script>

<button
    on:pointerdown={press}
    on:pointerup={release}
    on:pointerout={release}>
    <slot />
</button>

Read-only example component.svelte

<script>
    import { sws } from "main.ts";

    let sizeStore = sws.webSocketStore<number>("myList.size");
</script>

<div>
    {#each { length: $sizeStore } as _, index}
        <slot />
    {/each}
</div>

WebSocket Message Format

All communication between a server and this library is over WebSocket.

All WebSocket messages are interpreted as JSON objects.

The message object is defined as:

type Json = boolean | number | string | { [key: string]: Json } | Json[] | null;
type Message = {
    scope: string;
    id: string;
    value: Json;
}

The field scope identifies the scope of the client it comes from and limits which clients receive it when coming from the server. The field id is the primary identifier and determines where the value field is stored.

Client

Message Received

1. The incoming text data is parsed as JSON.
2. The object's scope field is checked if it is global ("global") or matches the client's local scope (for example "tp1"). If it does not match, the message is discarded.
3. The local Svelte store is indexed by the object's id field from the dictionary holding the respectively typed stores.
4. The store's value is assigned to the object's value field.

Server [^1]

Client Connected

1. Send the client messages for all the variables currently stored values

Message Received

1. The incoming text data is parsed as JSON.
2. The variable is indexed by the object's scope and id fields from the dictionary holding the respectively typed variables.
3. The variable's value is assigned to the object's value field.
4. Send all clients a message for the new value.
5. Handle any events.

[^1]: This is the behavior expected by this WebSocket client