bikeshaving/crank

Crank Component Authoring

This skill was built against the Crank version in its metadata. Always check npm for the latest version before generating code, as APIs may have changed.

JSX Template Tag (No Build Step)

Crank provides a jsx tagged template literal that runs directly in the browser with no transpiler, no bundler, and no build step. This is the recommended approach for single-file HTML artifacts, prototypes, and demos.

<!DOCTYPE html>
<html lang="en-US">
<head>
  <meta charset="utf-8" />
  <meta name="viewport" content="width=device-width" />
  <title>Crank App</title>
</head>
<body>
  <div id="app"></div>
  <script type="module">
    import {jsx, renderer} from "https://cdn.jsdelivr.net/npm/@b9g/crank/standalone.js";

    function *Counter() {
      let count = 0;
      const onclick = () => this.refresh(() => count++);

      for ({} of this) {
        yield jsx`
          <button onclick=${onclick}>Count: ${count}</button>
        `;
      }
    }

    renderer.render(jsx`<${Counter} />`, document.getElementById("app"));
  </script>
</body>
</html>

The standalone module exports both the jsx tag and the DOM renderer in a single import. For full documentation, see the JSX Template Tag guide.

With a Build Step (JSX syntax)

When using a bundler, you can use standard JSX syntax with the @jsxImportSource pragma:

/** @jsxImportSource @b9g/crank */
import {renderer} from "@b9g/crank/dom";

function *Timer({message}) {
  let seconds = 0;
  // Mount: start interval
  const interval = setInterval(() => this.refresh(() => seconds++), 1000);

  // Update: loop receives fresh props on each re-render
  for ({message} of this) {
    yield (
      <div>
        <p>{message}: {seconds}s</p>
        <button onclick={() => this.refresh(() => seconds = 0)}>Reset</button>
      </div>
    );
  }

  // Cleanup: runs on unmount
  clearInterval(interval);
}

renderer.render(<Timer message="Elapsed" />, document.getElementById("app"));

Not React — Quick Reference

React	Crank	Why
onClick	onclick	Lowercase DOM event names
onChange	onchange	Lowercase DOM event names
className	class	Standard HTML attributes
htmlFor	for	Standard HTML attributes
dangerouslySetInnerHTML	innerHTML	Direct DOM property
useState(init)	let x = init	Variable in generator scope
setState(val)	this.refresh(() => x = val)	Explicit refresh
useEffect(fn, [])	Code before first yield	Generator mount phase
useEffect(() => cleanup)	Code after for loop / this.cleanup(fn)	Generator cleanup
useRef(null)	let el = null + ref={n => el = n}	Variable + ref prop
useContext(ctx)	this.consume(key)	No Provider components
<Ctx.Provider value={v}>	this.provide(key, v)	Called in generator body

API Surface

These are the complete public exports.

// Core — components, elements, and rendering infrastructure
import {
  createElement,   // Create an element (called automatically by JSX)
  Fragment,         // Group children without a wrapper node ("")
  Portal,           // Render children into a different root node
  Copy,             // Reuse the previously rendered child tree
  Text,             // Render a text node with explicit text prop
  Raw,              // Insert raw HTML/markup via value prop
  Element,          // Element class (for type checking)
  isElement,        // Test if a value is a Crank element
  cloneElement,     // Clone an element with merged props
  Context,          // Component context class
  Renderer,         // Base renderer class (for custom renderers)
} from "@b9g/crank";

// DOM renderer
import {renderer, DOMRenderer} from "@b9g/crank/dom";

// HTML string renderer (SSR)
import {renderer as htmlRenderer, HTMLRenderer} from "@b9g/crank/html";

// JSX template tag (no build step)
import {jsx, html} from "@b9g/crank/jsx-tag";

// Standalone — re-exports everything above in one import
import {jsx, html, Fragment, renderer, domRenderer, htmlRenderer, DOMRenderer, HTMLRenderer} from "@b9g/crank/standalone";

Context methods (this inside generator components)

this.refresh(callback?)   // Mutate state and re-render
this.schedule(callback?)  // Run when this render's nodes exist, pre-DOM (once)
this.after(callback?)     // Run after this render is in the DOM (once)
this.cleanup(callback?)   // Run on unmount
this.consume(key)         // Read a provided value from an ancestor
this.provide(key, value)  // Provide a value to descendants
this.addEventListener(type, listener)    // Listen for DOM or custom events
this.removeEventListener(type, listener) // Remove an event listener
this.dispatchEvent(event)               // Dispatch an event up the tree

Philosophy

Crank components are plain JavaScript functions and generators. State is variables. Props are values. Updates are explicit.

• The framework preserves generator scope across yields — local variables are your state.
• this.refresh(() => { ... }) atomically mutates state and triggers a re-render.
• Props are plain values — destructure and transform them freely.
• Shared logic is plain classes, functions, and modules.
• Elements are immutable descriptions of what to render — never mutate an element or its props after creating it; build a new one instead.

JSX Template Tag — Quick Reference

jsx`
  <!-- host element -->
  <div />

  <!-- component element with shorthand close -->
  <${Component}>children<//>

  <!-- comment-style close -->
  <${Component}>children<//Component>

  <!-- fragment shorthand -->
  <>
    <p>first</p>
    <p>second</p>
  </>

  <!-- keyed fragment -->
  <${Fragment} key=${id}>
    <dt>${term}</dt>
    <dd>${definition}</dd>
  <//>

  <!-- boolean, string, interpolated string, expression, and spread props -->
  <input disabled type="text" class="a ${b} c" value=${val} ...${props} />

  <!-- namespaced props and tags -->
  <svg:circle attr:foo="bar" prop:value=${val} xlink:href="#icon" />

  <!-- conditional child -->
  ${show && jsx`<${Alert} message=${msg} />`}

  <!-- mapped children with keys -->
  ${items.map((d) => jsx`<li key=${d.id}>${d.name}</li>`)}

  <!-- commenting out a tree: expressions inside comments are discarded -->
  <!--
    <${Component} onclick=${handler}>
      <p>${text}</p>
    <//>
  -->
`

Multiple root elements are supported — the template tag automatically wraps them in a fragment.

References

Read these two files for complete API coverage and idiomatic patterns:

1. Component Specification — complete API reference: all component types, lifecycle, context methods, reconciliation, async behavior, special props, JSX modes
2. Style Guide — do/don’t patterns: component structure, state updates, props, cleanup, refs, error handling

Examples (consult as needed for the relevant task)

• Greeting — Hello world: functional components, props, composition
• TodoMVC — Full CRUD app: custom events, list management, filtering, localStorage
• Hacker News — Data dashboard: async fetching, hash routing, recursive tree rendering
• Password Strength — Interactive form widget: real-time validation, derived state, visual feedback
• Wizard — Multi-step form: stateful navigation, FormData collection, generator lifecycle
• Animated Letters — Animation: CSS transitions, exit animations, requestAnimationFrame

Additional Guides (for deeper reading on specific topics)

• Getting Started
• Elements
• Components
• Handling Events
• Async Components
• Special Props and Components
• Lifecycles
• Hydration
• Reusable Logic
• Working with TypeScript
• JSX Template Tag
• Reference for React Developers
• Custom Renderers

Blog Posts

• Introducing Crank
• Why Be Reactive?

Other

• Changelog