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ScaleJS Overview

ScaleJS is a template-first language that compiles .scale files into standalone custom elements. The compiler walks your markup, extracts state from an optional <script> block, and emits a self-updating web component class plus a runtime bundle. It favors HTML-centric authoring, Tailwind-friendly styling, and a predictable update cycle driven by dirty bitmasks.

Key ideas

  • Author components in plain HTML with single-brace expressions and block directives for control flow.
  • Define state, props, and methods with lightweight JavaScript inside <script>; ScaleJS hoists them into the generated class.
  • Compile-time Tailwind integration keeps your CSS scoped to the component without manual build wiring.
  • Output is a real custom element (Shadow DOM by default) with optional Light DOM and Shopify Liquid support.

From .scale to web component

  1. Write a .scale file that contains markup, optional <script>, and optional <style>.
  2. scalejs CLI parses the template, translates it into a render IR, and runs Tailwind against the collected class names.
  3. Code generation emits a custom element shell plus DOM block functions. State access is rewritten to this.state.* and instrumented with dirty flags.
  4. The compiler writes the JavaScript module (and optionally a Liquid section) to your target directory.

The generated element exposes prop accessors, lifecycle hooks, and helper utilities documented in the other guides.

Hello world example

<script>
  export let name = "Scale";
  function greet() {
    console.log(`Hello, ${name}!`);
  }
</script>

<section class="p-6 text-center">
  <h1 class="text-3xl font-bold">Hello {name}!</h1>
  <button class="mt-4 px-4 py-2 bg-neutral-900 text-white rounded" @click="greet()">
    Log greeting
  </button>
</section>

Save the file as components/hello.scale, then run:

npx scalejs build components/hello.scale --out dist/hello.js --tag scale-hello

The command writes a UMD-style bundle that defines <scale-hello> and injects component-scoped CSS. You can drop the script on any page and use the element:

<script src="/dist/hello.js" defer></script>
<scale-hello name="World"></scale-hello>

Runtime traits

  • Shadow DOM rendering is enabled by default; add light-dom to the element tag to render into the light DOM with attribute-based CSS scoping.
  • Props reflect to attributes (with boolean/number coercion) and can be updated imperatively through element properties.
  • The scheduler batches DOM work with requestAnimationFrame, recomputes derived state, then patches the block tree with dirty bitmasks.
  • Optional ig-bridge attribute installs a light-DOM mirror for Intelligems and similar integrations.

Continue with the remaining guides for template syntax, state management, and tooling details.