silmaril

Compile-time reactivity for JS

Install

npm install --save silmaril

yarn add silmaril

pnpm add silmaril

Features

• Compile-time reactivity
• Minimal reactive runtime
• Auto-memoization
• Stores

Requirement

Due to the compile-time nature of this library, it requires the use of Babel. silmaril provides a Babel plugin under silmaril/babel.

Usage

Basic reactivity

$$ defines the reactive boundary in your JS code. Any top-level variables (function-scoped) declared in $$ will be treated as "reactive" as possible. $ can be used to asynchronously react to variable changes.

Variable changes and reactions are only limited in $$ (even for nested $$ calls).

import { $$, $ } from 'silmaril';

$$(() => {
  // Create a "reactive" variable
  let count = 0;

  // Log count for changes
  $(console.log('Count: ', count));


  function multiply() {
    // Update count
    count *= 100;
  }

  multiply();
  // After some time, this code logs `Count: 100`.
});

$ will know which variables to track with, but it can only know if the variable is accessed in that same call.

import { $$, $ } from 'silmaril';

$$(() => {
  // Create a "reactive" variable
  let count = 0;
  let prefix = 'Count';

  function log(current) {
    // `prefix` is not tracked
    console.log(`${prefix}: `, current);
  }

  // This only tracks `count`
  $(log(count));
});

$ can also accept a function expression, and has the same tracking capabilities.

$(() => {
  // This tracks `count`
  console.log('Count:', count);
});

$ will only run if the tracked variables have actually changed (except for the first run), which means that it has some "auto-memoization".

Computed variables

If a reactive variable references another, the variable becomes computed, which means that it will re-evaluate everytime the referenced variables changes.

import { $$, $ } from 'silmaril';

$$(() => {
  // Create a "reactive" variable
  let count = 0;

  // Create a "reactive" const variable.
  const message = `Count: ${count}`;

  // This only tracks `message`
  $(console.log(message));

  count = 100; // Logs 'Count: 100'
});

Updates on computed variables are synchronous.

import { $$ } from 'silmaril';

$$(() => {
  let count = 0;
  const message = `Count: ${count}`;
  count = 100; // message = Count: 100
  count = 200; // message = Count: 200
});

Computed variables are also writable if declared with let.

import { $$, $sync } from 'silmaril';

$$(() => {
  let count = 0;
  let message = `Count: ${count}`;
  $sync(console.log('Log', message)); // Log Count: 0
  count = 100; // Log Count: 100
  message = 'Hello World'; // Log Hello World
  count = 200; // Log Count: 200
});

Lifecycles

onMount

onMount can be used to detect once $$ has finished the setup.

import { $$, onMount } from 'silmaril';

$$(() => {
  onMount(() => {
    console.log('Mounted!');
  });
  console.log('Not mounted yet!');
});

onMount can also be used in $, $sync, $composable and computed variables.

onDestroy

$$ returns a callback that allows disposing the reactive boundary. You can use onDestroy to detect when this happens.

import { $$, onDestroy } from 'silmaril';

const stop = $$(() => {
  onDestroy(() => {
    console.log('Destroyed!');
  });
});

// ...
stop();

onDestroy can also be used in $, $sync, $composable and computed variables.

Synchronous tracking

$ is deferred by a timeout schedule which means that $ asynchronously reacts on variable updates, this is so that updates on variables are batched by default (writing multiple times synchronously will only cause a single asynchronous update).

$sync provides synchronous tracking.

import { $$, $, $sync } from 'silmaril';

$$(() => {
  // Create a "reactive" variable
  let count = 0;

  // Create a "reactive" const variable.
  const message = `Count: ${count}`;

  $sync(console.log('Sync', message)); // Logs "Sync Count: 0"
  $(console.log('Async', message));

  count = 100; // Logs "Sync Count: 100"
  count = 200; // Logs "Sync Count: 200"

  // After some time the code ends, logs "Async Count: 200"
});

Stores

Reactivity is isolated in $$, but there are multiple ways to expose it outside $$ e.g. emulating event emitters, using observables, global state management, etc.

silmaril/store provides a simple API for this, and $store allows two-way (or one-way) binding for stores.

import { $$, $, $sync, $store } from 'silmaril';
import Store from 'silmaril/store';

// Create a store
const count = new Store(100);

// Subscribe to it
count.subscribe((current) => {
  console.log('Raw Count:', current);
});

$$(() => {
  // Bind the store to a reactive variable
  let current = $store(count);
  // `const` can also be used as an alternative
  // for enforcing one-way binding
  
  // Tracking the bound variable
  $sync(console.log('Sync Count:', current));
  $(console.log('Async Count:', current));

  // Mutate the variable (also mutates the store)
  current += 100;

  // Logs
  // Sync Count: 100
  // Raw Count: 200
  // Sync Count: 200
  // Async Count: 200
});

$store can accept any kind of implementation as long as it follows the following interface:

• subscribe(callback: Function): Function: accepts a callback and returns a cleanup callback
• get(): returns the current state of the store
• set(state): optional, mutates the state of the store.

Composition

$composable

$composable allows composing functions that can be used in $$, $sync, $, another $composable or computed variables.

import { $$, $sync, $composable, $store, onDestroy } from 'silmaril';
import Store from 'silmaril/store';

// Create a composable
const useSquared = $composable((store) => {
  // Bind the input store to a variable
  const input = $store(store);

  // Create a store
  const squaredStore = new Store(0);

  // Make sure to cleanup the store
  onDestroy(() => squaredStore.destroy());

  // Update the store based on the bound input store
  $sync(squaredStore.set(input ** 2));

  // Return the store
  return squaredStore;
});

$$(() => {
  // Create a store
  const store = new Store(0);

  // Bind it
  let input = $store(store);

  // Track the value of the store
  $sync(console.log('Value', input));

  // Create a "squared" store based on the input store
  // then bind it
  const squared = $store(useSquared(store));

  // Track the squared store
  $sync(console.log('Squared', squared));

  // Update the input store
  input = 100;

  // Logs
  // Count: 0
  // Count: 100
  // Count: 200
});

$ and $sync

Both $ and $sync behave much like $$: variables become reactive, onMount and onDestroy can be used, same goes to other APIs.

import { $$, $, onDestroy } from 'silmaril';

$$(() => {
  let y = 0;
  $(() => {
    let x = 0;

    $(console.log(x + y));

    onDestroy(() => {
      console.log('This will be cleaned up when `y` changes');
    });

    x += 100;
  });
  y += 100;
});

Inspirations/Prior Art

• Svelte
• Malina
• solid-labels
• Vue's Reactivity Transform

Sponsors

License

MIT © lxsmnsyc