Creating Rimitive Adapters

An adapter abstracts tree operations for any node-based rendering target. It decouples view modules (el(), map(), match()) from specific platforms, allowing the same view code to work with DOM, server rendering, Canvas, WebGL, terminals, or custom renderers.

Adapters are minimal by design—just 5 core tree operations plus optional lifecycle hooks.

The Adapter Interface

typescript

import type { Adapter, AdapterConfig } from '@rimitive/view/adapter';

type Adapter<TConfig extends AdapterConfig> = {
  // Core tree operations (required)
  createNode: (
    type: string,
    props?: Record<string, unknown>,
    parentContext?: ParentContext
  ) => TConfig['baseElement'];
  setAttribute: (
    node: TConfig['baseElement'],
    key: string,
    value: unknown
  ) => void;
  appendChild: (
    parent: TConfig['baseElement'],
    child: TConfig['baseElement']
  ) => void;
  removeChild: (
    parent: TConfig['baseElement'],
    child: TConfig['baseElement']
  ) => void;
  insertBefore: (
    parent: TConfig['baseElement'],
    child: TConfig['baseElement'],
    reference: TConfig['baseElement'] | null
  ) => void;

  // Lifecycle hooks (optional)
  beforeCreate?: (type: string, props?: Record<string, unknown>) => void;
  onCreate?: (ref: NodeRef, parent: TConfig['baseElement']) => void;
  beforeAttach?: (
    ref: NodeRef,
    parent: TConfig['baseElement'],
    nextSibling: TConfig['baseElement'] | null
  ) => void;
  onAttach?: (ref: NodeRef, parent: TConfig['baseElement']) => void;
  beforeDestroy?: (ref: NodeRef, parent: TConfig['baseElement']) => void;
  onDestroy?: (ref: NodeRef, parent: TConfig['baseElement']) => void;
};

AdapterConfig Type

Define types for your adapter to get autocomplete in el():

typescript

type AdapterConfig = {
  props: object; // Maps tag names to prop types
  elements: object; // Maps tag names to node types
  events: object; // Maps event names to event types
  baseElement: object; // Base node type for this adapter
};

Minimal Adapter Example

A simple in-memory adapter for testing or non-DOM environments:

typescript

import type { Adapter, AdapterConfig } from '@rimitive/view/adapter';

type SimpleNode = {
  type: string;
  props: Record<string, unknown>;
  children: SimpleNode[];
};

type SimpleAdapterConfig = AdapterConfig & {
  props: Record<string, Record<string, unknown>>;
  elements: Record<string, SimpleNode>;
  events: Record<string, Event>;
  baseElement: SimpleNode;
};

function createSimpleAdapter(): Adapter<SimpleAdapterConfig> {
  return {
    createNode: (type, props) => ({
      type,
      props: { ...props },
      children: [],
    }),

    setAttribute: (node, key, value) => {
      node.props[key] = value;
    },

    appendChild: (parent, child) => {
      parent.children.push(child);
    },

    removeChild: (parent, child) => {
      const idx = parent.children.indexOf(child);
      if (idx !== -1) parent.children.splice(idx, 1);
    },

    insertBefore: (parent, child, reference) => {
      if (reference === null) {
        parent.children.push(child);
      } else {
        const idx = parent.children.indexOf(reference);
        if (idx !== -1) {
          parent.children.splice(idx, 0, child);
        } else {
          parent.children.push(child);
        }
      }
    },
  };
}

Canvas Adapter Example

A more complex adapter for 2D canvas rendering:

typescript

import type { Adapter, AdapterConfig } from '@rimitive/view/adapter';

type CanvasNode = {
  type: 'rect' | 'circle' | 'text' | 'group';
  x: number;
  y: number;
  width?: number;
  height?: number;
  radius?: number;
  fill?: string;
  stroke?: string;
  value?: string;
  children: CanvasNode[];
  parent: CanvasNode | null;
};

type CanvasAdapterConfig = AdapterConfig & {
  props: {
    rect: {
      x?: number;
      y?: number;
      width?: number;
      height?: number;
      fill?: string;
    };
    circle: { x?: number; y?: number; radius?: number; fill?: string };
    text: { x?: number; y?: number; value?: string; fill?: string };
    group: { x?: number; y?: number };
  };
  elements: {
    rect: CanvasNode;
    circle: CanvasNode;
    text: CanvasNode;
    group: CanvasNode;
  };
  events: Record<string, never>;
  baseElement: CanvasNode;
};

function createCanvasAdapter(
  ctx: CanvasRenderingContext2D
): Adapter<CanvasAdapterConfig> {
  let needsRedraw = false;
  let root: CanvasNode | null = null;

  function scheduleRedraw() {
    if (needsRedraw) return;
    needsRedraw = true;
    requestAnimationFrame(() => {
      needsRedraw = false;
      if (root) render(root);
    });
  }

  function render(node: CanvasNode, offsetX = 0, offsetY = 0) {
    const x = (node.x ?? 0) + offsetX;
    const y = (node.y ?? 0) + offsetY;

    switch (node.type) {
      case 'rect':
        if (node.fill) {
          ctx.fillStyle = node.fill;
          ctx.fillRect(x, y, node.width ?? 0, node.height ?? 0);
        }
        break;
      case 'circle':
        ctx.beginPath();
        ctx.arc(x, y, node.radius ?? 0, 0, Math.PI * 2);
        if (node.fill) {
          ctx.fillStyle = node.fill;
          ctx.fill();
        }
        break;
      case 'text':
        if (node.fill) ctx.fillStyle = node.fill;
        ctx.fillText(node.value ?? '', x, y);
        break;
    }

    for (const child of node.children) {
      render(child, x, y);
    }
  }

  return {
    createNode: (type, props) => {
      const node: CanvasNode = {
        type: type as CanvasNode['type'],
        x: 0,
        y: 0,
        children: [],
        parent: null,
        ...props,
      };
      return node;
    },

    setAttribute: (node, key, value) => {
      (node as Record<string, unknown>)[key] = value;
      scheduleRedraw();
    },

    appendChild: (parent, child) => {
      child.parent = parent;
      parent.children.push(child);
      if (!root) root = parent;
      scheduleRedraw();
    },

    removeChild: (parent, child) => {
      const idx = parent.children.indexOf(child);
      if (idx !== -1) {
        parent.children.splice(idx, 1);
        child.parent = null;
      }
      scheduleRedraw();
    },

    insertBefore: (parent, child, reference) => {
      child.parent = parent;
      if (reference === null) {
        parent.children.push(child);
      } else {
        const idx = parent.children.indexOf(reference);
        parent.children.splice(
          idx !== -1 ? idx : parent.children.length,
          0,
          child
        );
      }
      if (!root) root = parent;
      scheduleRedraw();
    },
  };
}

Using Adapters with View Modules

Pass your adapter to view module factories:

typescript

import { compose } from '@rimitive/core';
import {
  SignalModule,
  ComputedModule,
  EffectModule,
} from '@rimitive/signals/extend';
import { createElModule } from '@rimitive/view/el';
import { createMapModule } from '@rimitive/view/map';
import { createMatchModule } from '@rimitive/view/match';
import { MountModule } from '@rimitive/view/deps/mount';

// Create your adapter
const adapter = createCanvasAdapter(ctx);

// Compose with view modules
const svc = compose(
  SignalModule,
  ComputedModule,
  EffectModule,
  createElModule(adapter),
  createMapModule(adapter),
  createMatchModule(adapter),
  MountModule
);

const { el, map, mount } = svc;

// Now el() creates canvas nodes instead of DOM nodes
const scene = el('group')(
  el('rect').props({ x: 10, y: 10, width: 100, height: 50, fill: 'blue' }),
  el('circle').props({ x: 200, y: 50, radius: 25, fill: 'red' })
);

Lifecycle Hooks

Use lifecycle hooks for advanced use cases:

Hook	When	Use Cases
`beforeCreate`	Before node creation	Hydration position setup
`onCreate`	After node ref created	SSR markers, position sync
`beforeAttach`	Before content attached	Hydration positioning
`onAttach`	After content attached	SSR fragments, lifecycle callbacks
`beforeDestroy`	Before removal	Exit animations
`onDestroy`	After removal	Final cleanup

Animation Example

typescript

const animatedAdapter: Adapter<DOMAdapterConfig> = {
  ...createDOMAdapter(),

  beforeDestroy: (ref, parent) => {
    if (ref.element instanceof HTMLElement) {
      ref.element.classList.add('exiting');
      // Note: actual animation delay requires more infrastructure
    }
  },

  onDestroy: (ref, parent) => {
    console.log('Node removed:', ref.element);
  },
};

Cross-Renderer Composition

The parentContext parameter in createNode enables nested renderers:

typescript

createNode: (type, props, parentContext) => {
  // parentContext.element is the parent node
  // parentContext.adapter is the parent's adapter (if different)

  // A canvas adapter nested in DOM could create a <canvas> element
  // when it detects a DOM parent context
  if (parentContext?.adapter !== this && type === 'canvas-root') {
    return document.createElement('canvas');
  }

  return createCanvasNode(type, props);
};

Built-in Adapters

Rimitive provides these adapters:

Adapter	Import	Purpose
DOM	`@rimitive/view/adapters/dom`	Browser rendering
Test	`@rimitive/view/adapters/test`	Unit testing (no DOM)
Server	`@rimitive/ssr`	Server-side rendering
Hydration	`@rimitive/ssr`	Rehydrating server HTML

Testing Custom Adapters

Use the test adapter pattern for adapter tests:

typescript

import { describe, it, expect } from 'vitest';

describe('CanvasAdapter', () => {
  it('creates nodes with correct type', () => {
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d')!;
    const adapter = createCanvasAdapter(ctx);

    const rect = adapter.createNode('rect', { x: 10, y: 20 });

    expect(rect.type).toBe('rect');
    expect(rect.x).toBe(10);
    expect(rect.y).toBe(20);
  });

  it('builds tree structure', () => {
    const adapter = createCanvasAdapter(ctx);
    const group = adapter.createNode('group');
    const rect = adapter.createNode('rect');

    adapter.appendChild(group, rect);

    expect(group.children).toContain(rect);
    expect(rect.parent).toBe(group);
  });
});

Hydration Adapter Pattern

The hydration adapter demonstrates a fundamentally different approach: reusing existing DOM instead of creating new nodes. This is essential for SSR where the HTML already exists.

Key differences from standard adapters:

•createNode walks existing DOM instead of creating elements
•Position tracking via a mutable path[] array
•Structure validation throws HydrationMismatch on mismatches
•Fragment marker handling skips SSR comment markers

typescript

import type { Adapter } from '@rimitive/view/adapter';
import type { DOMAdapterConfig } from '@rimitive/view/adapters/dom';

class HydrationMismatch extends Error {
  constructor(message: string) {
    super(message);
    this.name = 'HydrationMismatch';
  }
}

function createHydrationAdapter(
  containerEl: HTMLElement
): Adapter<DOMAdapterConfig> {
  // Mutable position - path[i] is child index at depth i
  const path: number[] = [];

  function getNodeAtPath(root: Node, indices: number[]): Node {
    let node = root;
    for (const index of indices) {
      node = node.childNodes[index];
      if (!node) throw new HydrationMismatch(`No child at index ${index}`);
    }
    return node;
  }

  return {
    createNode: (type, props) => {
      // Text nodes - reuse existing
      if (type === 'text') {
        const node = getNodeAtPath(containerEl, path);
        if (node.nodeType !== 3) {
          throw new HydrationMismatch(`Expected text, got ${node.nodeName}`);
        }
        // Update text if needed
        const text = (props?.value as string) ?? '';
        if (node.textContent !== text) node.textContent = text;
        // Advance to next sibling
        path[path.length - 1]++;
        return node;
      }

      // Element nodes - validate and reuse
      const node = getNodeAtPath(containerEl, path);
      if (
        node.nodeType !== 1 ||
        (node as Element).tagName.toLowerCase() !== type
      ) {
        throw new HydrationMismatch(
          `Expected <${type}>, got <${(node as Element).tagName}>`
        );
      }
      // Enter element's children
      path.push(0);
      return node;
    },

    setAttribute: (node, key, value) => {
      // Attach event handlers and update dynamic props
      if (node.nodeType === 3 && key === 'value') {
        node.textContent = String(value);
        return;
      }
      Reflect.set(node, key, value);
    },

    appendChild: (parent, child) => {
      // Element already attached - this is the "exit" signal
      if (child.nodeType === 1 && child.parentNode === parent) {
        path.pop(); // Exit element's children
        path[path.length - 1]++; // Advance to next sibling
      }
    },

    removeChild: () => {}, // No-op during hydration

    insertBefore: (parent, child) => {
      // Same exit signal as appendChild
      if (child.nodeType === 1 && child.parentNode === parent) {
        path.pop();
        path[path.length - 1]++;
      }
    },
  };
}

Mode Switching

After hydration completes, switch to a standard adapter for dynamic updates:

typescript

function createSwitchableAdapter(
  hydrateAdapter: Adapter<DOMAdapterConfig>,
  fallbackAdapter: Adapter<DOMAdapterConfig>
): Adapter<DOMAdapterConfig> & { switchToFallback: () => void } {
  let current = hydrateAdapter;

  return {
    createNode: (type, props) => current.createNode(type, props),
    setAttribute: (node, key, value) => current.setAttribute(node, key, value),
    appendChild: (parent, child) => current.appendChild(parent, child),
    removeChild: (parent, child) => current.removeChild(parent, child),
    insertBefore: (parent, child, ref) =>
      current.insertBefore(parent, child, ref),

    switchToFallback: () => {
      current = fallbackAdapter;
    },
  };
}

// Usage
const adapter = createSwitchableAdapter(
  createHydrationAdapter(container),
  createDOMAdapter()
);

// After hydration
adapter.switchToFallback();

When to Create a Custom Adapter

Good candidates:

•Canvas/WebGL rendering
•Terminal/CLI interfaces
•Native mobile (React Native-style)
•Game engines
•PDF generation
•Custom component systems
•Hydration for custom SSR solutions

Not necessary for:

•Standard web apps (use DOM adapter)
•Server rendering (use SSR adapter)
•Testing (use test adapter)
•Standard hydration (use @rimitive/ssr)