Unified Full-Stack Panel Authoring

One guide for the complete workflow: backend route → service → server wiring → Panel component with resilience → registration. Eliminates the need to consult separate skills for what is always a single cohesive task.

---

When to Use

• Adding a new panel type to a vanilla-TypeScript dashboard
• Creating a feature that spans all layers: server route, service, component, registration
• Ensuring pattern-consistency across the stack
• Projects using a manual http.createServer dispatch loop or Express

---

Quick Reference — File Checklist

#	File	Action
1	server/routes/{feature}-route.ts	Create
2	src/services/{feature}.ts	Create
3	src/components/{Feature}Panel.ts	Create
4	src/components/index.ts	Update — add export
5	server/index.ts	Update — import + dispatch case
6	src/utils/circuit-breaker.ts	Create if absent
7	src/utils/sparkline.ts	Create if absent

---

Step 1 — Explore Project Structure

Run these commands before writing a single line of code. Reading existing patterns prevents style drift and reveals the exact dispatch mechanism.

# Locate server entry point (critical for wiring)
find . -name "index.ts" -o -name "index.js" -o -name "server.ts" -o -name "server.js" \
  | grep -v node_modules | head -10

# Find existing route handlers to use as pattern files
find server/routes -name "*.ts" -o -name "*.js" 2>/dev/null | head -10

# Find existing service files
find src/services -name "*.ts" -o -name "*.js" 2>/dev/null | head -10

# Find existing Panel components
find src/components -name "*Panel.ts" 2>/dev/null | head -10

# Find the Panel base class
find src -name "Panel.ts" 2>/dev/null | head -5

# Find component registration index
find src/components -name "index.ts" 2>/dev/null | head -3

# Check for CircuitBreaker utility
find src/utils -name "circuit-breaker.ts" 2>/dev/null

# Check framework (should NOT find React in vanilla TS projects)
grep -s '"react"' package.json | head -3

Read 1-2 examples from each layer before generating any code:

cat server/routes/<existing>-route.ts
cat src/services/<existing>.ts
cat src/components/<existing>Panel.ts
cat src/components/index.ts
cat server/index.ts          # most important: reveals dispatch pattern

---

Step 2 — Detect Server Dispatch Pattern

Read server/index.ts (or server/index.js, src/server.ts) and classify:

# Express signals
grep -n "express\|app\.use\|router\." server/index.ts 2>/dev/null

# Manual http.createServer signals
grep -n "createServer\|switch.*url\|switch.*pathname\|req\.url\|case '/" server/index.ts 2>/dev/null

Pattern in file	Wiring method (Step 5)
app.use('/api/x', xRouter)	5A - Express
switch(pathname) { case '/api/x':	5B - Manual switch/case
if (url.startsWith('/api/x'))	5C - Manual if/else chain
const handlers = { '/api/x': fn }	5D - Handler map

NOTE: Misidentifying the dispatch pattern is the most common cause of silent 404s. If unsure, read the full server entry point before proceeding.

---

Step 3 — Create the Server Route Handler

Use the manual dispatch template for http.createServer projects (most common in this codebase). Use the Express template only when Express is confirmed.

Manual dispatch (TypeScript) — preferred template

// server/routes/{feature}-route.ts
import { IncomingMessage, ServerResponse } from 'http';
import { fetch{Feature}Data } from '../../src/services/{feature}';

export async function handle{Feature}Request(
  req: IncomingMessage,
  res: ServerResponse,
  action?: string
): Promise<void> {
  try {
    const data = await fetch{Feature}Data(action);
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ success: true, data }));
  } catch (err) {
    res.writeHead(500, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({
      success: false,
      error: err instanceof Error ? err.message : String(err)
    }));
  }
}

Express template (only when confirmed)

// server/routes/{feature}-route.ts
import { Router } from 'express';
import { fetch{Feature}Data } from '../../src/services/{feature}';

const router = Router();

router.get('/', async (req, res) => {
  try {
    const data = await fetch{Feature}Data(req.query.action as string | undefined);
    res.json({ success: true, data });
  } catch (err) {
    res.status(500).json({ success: false, error: (err as Error).message });
  }
});

export default router;

---

Step 4 — Create the Service Layer

The service owns data fetching and transformation. The CircuitBreaker (Step 6) wraps the service call at the component level — keep the service itself simple.

// src/services/{feature}.ts

export interface {Feature}Item {
  id: string;
  // define your data shape matching the API response
}

/**
 * Fetch {feature} data from the server API.
 * @param action  Optional sub-action / filter parameter.
 */
export async function fetch{Feature}Data(action?: string): Promise<{Feature}Item[]> {
  const url = `/api/panels/{feature}${action ? `?action=${encodeURIComponent(action)}` : ''}`;
  const res = await fetch(url, {
    headers: { Authorization: `Bearer ${localStorage.getItem('token') ?? ''}` }
  });
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  const { data } = await res.json() as { data: {Feature}Item[] };
  return data;
}

---

Step 5 — Wire the Route Handler into the Server

This step is the most frequently missed and causes features to silently return 404.

After creating the route file, open server/index.ts and add both an import and a dispatch entry.

5A - Express

// server/index.ts  -- excerpt
import {feature}Router from './routes/{feature}-route';

// Add alongside other app.use() calls:
app.use('/api/panels/{feature}', {feature}Router);

5B - Manual switch/case (most common pattern)

// server/index.ts  -- excerpt showing the additions

// 1. Add import near the top with other route imports
import { handle{Feature}Request } from './routes/{feature}-route';

// 2. Inside the switch / if-else dispatch block, add a new case
// Find the block that looks like:
//   switch (pathname) {
//     case '/api/panels/health': ...
//     case '/api/panels/email':  ...
// Add:
    case '/api/panels/{feature}':
      await handle{Feature}Request(req, res, action);
      break;

5C - Manual if/else chain

// server/index.ts  -- excerpt
import { handle{Feature}Request } from './routes/{feature}-route';

// Add a new else-if branch:
} else if (url.startsWith('/api/panels/{feature}')) {
  await handle{Feature}Request(req, res, action);
}

5D - Handler map

// server/index.ts  -- excerpt
import { handle{Feature}Request } from './routes/{feature}-route';

const handlers: Record<string, HandlerFn> = {
  // ... existing entries ...
  '/api/panels/{feature}': handle{Feature}Request,
};

Verification: After wiring, start the server and curl /api/panels/{feature} — you should receive JSON, not a 404.

---

Step 6 — Create the Panel Component

Architecture overview

Panel (base class)
+-- element: HTMLElement (.panel)
    +-- header (.panel-header)
    |   +-- headerLeft (.panel-header-left)
    |   |   +-- title (.panel-title)
    |   +-- countEl (.panel-count)  [optional]
    +-- content (.panel-content)

Resilience layers

Layer	When to use
isFetching guard	Always -- prevents duplicate concurrent requests
fetchWithRetry()	When you own the raw fetch and want per-request retry
CircuitBreaker.execute()	When a service may fail repeatedly; serves stale cache during cooldown
saveState() / loadState()	When collapsed/size state should survive page reloads

Complete Panel component template

// src/components/{Feature}Panel.ts
import { Panel } from './Panel';
import { createCircuitBreaker } from '../utils/circuit-breaker';
import { fetch{Feature}Data, {Feature}Item } from '../services/{feature}';

// Module-level breaker -- persists cache and failure state between re-renders
const breaker = createCircuitBreaker<{Feature}Item[]>({
  name: '{Feature}',
  cacheTtlMs: 60_000,      // serve cache for 1 min
  cooldownMs: 5 * 60_000,  // open circuit for 5 min after maxFailures
  maxFailures: 2,
});

export class {Feature}Panel extends Panel {
  private refreshTimer: ReturnType<typeof setInterval> | null = null;

  constructor() {
    super({ id: '{feature}', title: '{Feature Display Name}', showCount: true });
    this.loadState();                                  // restore collapsed/size
    this.fetchData();
    this.refreshTimer = setInterval(() => this.fetchData(), 60_000);
  }

  private async fetchData(): Promise<void> {
    if (this.isFetching) return;
    this.setFetching(true);
    try {
      // One-liner: wraps existing service call with caching + circuit-break
      const items = await breaker.execute(() => fetch{Feature}Data(), []);
      this.setCount(items.length);
      this.render(items);
    } catch (err) {
      this.showError(
        err instanceof Error ? err.message : 'Failed to load',
        () => {
          this.retryAttempts = 0;
          this.retryDelay = 1000;
          this.fetchData();
        }
      );
    } finally {
      this.setFetching(false);
    }
  }

  private render(items: {Feature}Item[]): void {
    if (items.length === 0) {
      this.setContent('<div class="panel-empty">No items found.</div>');
      return;
    }

    const container = document.createElement('div');
    container.className = '{feature}-panel';

    for (const item of items) {
      const row = document.createElement('div');
      row.className = '{feature}-panel__row';
      // Build DOM from item fields -- no JSX, no innerHTML with untrusted data:
      const label = document.createElement('span');
      label.className = '{feature}-panel__label';
      label.textContent = item.id;          // replace with real fields
      row.appendChild(label);
      container.appendChild(row);
    }

    this.content.innerHTML = '';
    this.content.appendChild(container);
    this.saveState();
  }

  destroy(): void {
    if (this.refreshTimer !== null) clearInterval(this.refreshTimer);
    super.destroy();
  }
}

Key rules for vanilla TS panels (no React):

• Extend Panel base class; use setContent() / showError() / setCount() / showLoading() instead of React state.
• Build DOM via document.createElement -- not JSX, not innerHTML with untrusted strings.
• Lifecycle: constructor -> fetchData() -> render() -> destroy(). No useEffect.
• File extension is .ts, not .jsx/.tsx.

---

Step 7 — Register the Component in index.ts

Export the new panel from the components barrel file so the dashboard can discover it.

// src/components/index.ts  -- add alongside existing exports
export { {Feature}Panel } from './{Feature}Panel';

Then instantiate and mount in the dashboard bootstrap (follow the existing pattern):

// src/index.ts or src/dashboard.ts  -- excerpt
import { {Feature}Panel } from './components';

const {feature}Panel = new {Feature}Panel();
document.getElementById('{feature}-slot')?.appendChild({feature}Panel.getElement());

---

Step 8 — Add Utility Files (if absent)

Only create these if find src/utils -name "circuit-breaker.ts" returns nothing.

src/utils/circuit-breaker.ts

interface CircuitState { failures: number; cooldownUntil: number; }
interface CacheEntry<T> { data: T; timestamp: number; }

export interface CircuitBreakerOptions {
  name: string;
  maxFailures?: number;  // default 2
  cooldownMs?: number;   // default 5 min
  cacheTtlMs?: number;   // default 10 min
}

export class CircuitBreaker<T> {
  private state: CircuitState = { failures: 0, cooldownUntil: 0 };
  private cache: CacheEntry<T> | null = null;
  private readonly name: string;
  private readonly maxFailures: number;
  private readonly cooldownMs: number;
  private readonly cacheTtlMs: number;

  constructor(options: CircuitBreakerOptions) {
    this.name        = options.name;
    this.maxFailures = options.maxFailures ?? 2;
    this.cooldownMs  = options.cooldownMs  ?? 5 * 60 * 1000;
    this.cacheTtlMs  = options.cacheTtlMs  ?? 10 * 60 * 1000;
  }

  isOnCooldown(): boolean {
    if (Date.now() < this.state.cooldownUntil) return true;
    if (this.state.cooldownUntil > 0) this.state = { failures: 0, cooldownUntil: 0 };
    return false;
  }

  getCached(): T | null {
    if (this.cache && Date.now() - this.cache.timestamp < this.cacheTtlMs) return this.cache.data;
    return null;
  }

  recordSuccess(data: T): void {
    this.state = { failures: 0, cooldownUntil: 0 };
    this.cache = { data, timestamp: Date.now() };
  }

  recordFailure(): void {
    this.state.failures++;
    if (this.state.failures >= this.maxFailures) {
      this.state.cooldownUntil = Date.now() + this.cooldownMs;
      console.warn(`[${this.name}] Circuit open -- cooldown ${this.cooldownMs / 1000}s`);
    }
  }

  async execute<R extends T>(fn: () => Promise<R>, defaultValue: R): Promise<R> {
    if (this.isOnCooldown()) return (this.getCached() as R) ?? defaultValue;
    const cached = this.getCached();
    if (cached !== null) return cached as R;
    try {
      const result = await fn();
      this.recordSuccess(result);
      return result;
    } catch (e) {
      console.error(`[${this.name}] Request failed:`, e);
      this.recordFailure();
      return defaultValue;
    }
  }
}

export function createCircuitBreaker<T>(options: CircuitBreakerOptions): CircuitBreaker<T> {
  return new CircuitBreaker<T>(options);
}

src/utils/sparkline.ts (optional — for numeric trend data)

/**
 * Returns an inline SVG sparkline string, or '' if data is too short.
 * Embed directly in HTML template strings.
 */
export function miniSparkline(
  data: number[] | undefined,
  change: number | null,
  w = 50,
  h = 16
): string {
  if (!data || data.length < 2) return '';
  const min   = Math.min(...data);
  const max   = Math.max(...data);
  const range = max - min || 1;
  const color = change != null && change >= 0 ? 'var(--green)' : 'var(--red)';
  const points = data.map((v, i) => {
    const x = (i / (data.length - 1)) * w;
    const y = h - ((v - min) / range) * (h - 2) - 1;
    return `${x.toFixed(1)},${y.toFixed(1)}`;
  }).join(' ');
  return `<svg width="${w}" height="${h}" viewBox="0 0 ${w} ${h}">` +
    `<polyline points="${points}" fill="none" stroke="${color}" ` +
    `stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"/></svg>`;
}

---

Step 9 — Panel Base Class (if absent)

Only create src/components/Panel.ts if no existing base class is found.

// src/components/Panel.ts
export interface PanelOptions {
  id: string;
  title: string;
  showCount?: boolean;
  className?: string;
}

export class Panel {
  protected element: HTMLElement;
  protected content: HTMLElement;
  protected header: HTMLElement;
  protected countEl: HTMLElement | null = null;
  protected panelId: string;
  private _fetching = false;

  // Retry state (used by fetchWithRetry)
  protected retryAttempts = 0;
  protected retryDelay = 1000;
  private maxRetries = 3;

  constructor(options: PanelOptions) {
    this.panelId = options.id;
    this.element = document.createElement('div');
    this.element.className = `panel ${options.className ?? ''}`;
    this.element.dataset.panel = options.id;

    this.header = document.createElement('div');
    this.header.className = 'panel-header';

    const headerLeft = document.createElement('div');
    headerLeft.className = 'panel-header-left';
    const title = document.createElement('span');
    title.className = 'panel-title';
    title.textContent = options.title;
    headerLeft.appendChild(title);
    this.header.appendChild(headerLeft);

    if (options.showCount) {
      this.countEl = document.createElement('span');
      this.countEl.className = 'panel-count';
      this.countEl.textContent = '0';
      this.header.appendChild(this.countEl);
    }

    this.content = document.createElement('div');
    this.content.className = 'panel-content';
    this.content.id = `${options.id}Content`;

    this.element.appendChild(this.header);
    this.element.appendChild(this.content);
    this.showLoading();
  }

  public getElement(): HTMLElement { return this.element; }

  public showLoading(message = 'Loading...'): void {
    this.content.innerHTML = `
      <div class="panel-loading">
        <div class="panel-loading-spinner"></div>
        <div class="panel-loading-text">${message}</div>
      </div>`;
  }

  public showError(message = 'Failed to load', onRetry?: () => void): void {
    this.content.innerHTML = `
      <div class="panel-error-state">
        <div class="panel-error-msg">${message}</div>
        ${onRetry ? '<button class="panel-retry-btn" data-panel-retry>Retry</button>' : ''}
      </div>`;
    if (onRetry) {
      this.content.querySelector('[data-panel-retry]')?.addEventListener('click', onRetry);
    }
  }

  public setContent(html: string): void { this.content.innerHTML = html; }

  public setCount(count: number): void {
    if (this.countEl) this.countEl.textContent = count.toString();
  }

  public show(): void { this.element.classList.remove('hidden'); }
  public hide(): void { this.element.classList.add('hidden'); }
  public destroy(): void { this.element.remove(); }

  protected setFetching(v: boolean): void { this._fetching = v; }
  protected get isFetching(): boolean { return this._fetching; }

  protected async fetchWithRetry(url: string): Promise<unknown> {
    while (this.retryAttempts < this.maxRetries) {
      try {
        const response = await fetch(url);
        if (!response.ok) throw new Error(`HTTP ${response.status}`);
        return await response.json();
      } catch (error) {
        this.retryAttempts++;
        if (this.retryAttempts >= this.maxRetries) {
          throw new Error(`Failed after ${this.maxRetries} attempts: ${(error as Error).message}`);
        }
        await new Promise(resolve => setTimeout(resolve, this.retryDelay));
        this.retryDelay *= 2;
      }
    }
  }

  public saveState(): void {
    localStorage.setItem(`panelState_${this.panelId}`, JSON.stringify({
      isExpanded: !this.element.classList.contains('collapsed'),
      width: this.element.style.width,
      height: this.element.style.height,
    }));
  }

  public loadState(): void {
    const raw = localStorage.getItem(`panelState_${this.panelId}`);
    if (!raw) return;
    const { isExpanded, width, height } = JSON.parse(raw) as {
      isExpanded: boolean; width: string; height: string;
    };
    if (!isExpanded) this.element.classList.add('collapsed');
    if (width)  this.element.style.width  = width;
    if (height) this.element.style.height = height;
  }
}

---

Step 10 — Safe File Writing

Known tool issue: write_file (and some shell tools) fail silently or with "unknown error" when file content contains multi-byte Unicode characters such as emoji (e.g., document, chart, checkmark emoji).

Rules for safe content

1. Never use emoji in generated source code. Replace with plain-text equivalents:

   • Document emoji -> [doc] or (file)
   • Chart emoji -> [chart]
   • Checkmark emoji -> [ok] or (done)
   • Warning emoji -> [warn] or WARNING:

2. Use ASCII substitutes in comments instead of Unicode box-drawing characters.

3. Test-write suspect content to a throwaway file first if unsure:

   echo "test content" > /tmp/write_test.txt && cat /tmp/write_test.txt
   

4. Recovery pattern -- if a write_file call fails:

   • Strip all non-ASCII characters from the content.
   • Retry the write.
   • If still failing, split the file into smaller chunks and concatenate with cat.

---

Validation Checklist

Before considering the feature complete, verify each layer:

Server route
  [ ] File created at server/routes/{feature}-route.ts
  [ ] Exports handle{Feature}Request function
  [ ] Returns { success: true, data } on success
  [ ] Returns { success: false, error } on failure with correct HTTP status

Service
  [ ] File created at src/services/{feature}.ts
  [ ] Exports fetch{Feature}Data function
  [ ] Throws on non-ok HTTP status (so CircuitBreaker can record failures)

Server wiring
  [ ] Import added to server/index.ts
  [ ] Dispatch case/route added (matching the detected pattern)
  [ ] curl /api/panels/{feature} returns JSON (not 404)

Panel component
  [ ] Extends Panel base class
  [ ] Uses isFetching guard
  [ ] CircuitBreaker wraps the service call
  [ ] showError() called with retry callback on failure
  [ ] destroy() clears interval and calls super.destroy()

Registration
  [ ] Export added to src/components/index.ts
  [ ] Panel instantiated and mounted in dashboard bootstrap

File safety
  [ ] No emoji in any generated source file
  [ ] All write_file calls succeeded (check file size > 0)

---

Common Mistakes

Mistake	Symptom	Fix
Skipping Step 5 (server wiring)	Feature returns 404	Add import + dispatch entry to server/index.ts
Wrong dispatch pattern	404 or runtime error	Re-read server/index.ts; use grep from Step 2
Emoji in source files	write_file silent failure	Replace all emoji with ASCII equivalents
React template in vanilla TS project	Compile errors	Confirm no React in package.json; use Panel base class template
Creating Panel.ts when one exists	Overwrites base class	Check with find src -name "Panel.ts" first
Not calling super.destroy()	Memory leak	Always chain super.destroy() in subclass destroy()
CircuitBreaker declared inside class	Cache lost between fetches	Declare const breaker = ... at module level outside the class