Implement Chrome Extension Side Panel (Chrome) Turnkey

Popup windows of Chrome extensions close when clicking outside them — this is critical for tools requiring constant access. Side Panel API solves this problem by providing a persistent side panel. Users of extensions for notes, monitoring, or devtools often lose data when accidentally closing Popup. Side Panel remains open, preserving state when switching tabs. We implement such panels turnkey in 3–9 days. We will evaluate your project — contact us. Our experience with Chrome API is over 5 years, we guarantee post-launch support. Get a consultation on integration.

According to Side Panel API, the panel can be configured individually for each tab. In one project, we replaced Popup with Side Panel for a CRM extension. Users stopped losing active orders when switching tabs, and time spent working with the extension increased by 40%.

How Side Panel solves the context loss problem?

Popup lives only while the tab is active and the user hasn't clicked outside the window. Side Panel remains open when switching tabs and even when working in another window. This is critical for DevTools-like extensions, monitoring, notes, and chats. Switching between tabs does not require reloading the panel — data is preserved in memory.

Differences between Side Panel and Popup

How to configure Side Panel for different tabs?

The panel can be different for each tab or common for all. This is set via chrome.sidePanel.setOptions with the tabId parameter. For example, for GitHub we display a panel with tasks, for Figma — with comments, for others — disable it. Resource savings: the panel does not load on unnecessary sites.

Manifest V3 setup

{
  "manifest_version": 3,
  "name": "My Side Panel Extension",
  "version": "1.0.0",
  "permissions": ["storage", "tabs", "activeTab", "scripting", "sidePanel"],
  "background": {
    "service_worker": "background.js"
  },
  "action": {
    "default_icon": "icons/icon48.png",
    "default_title": "Open panel"
  },
  "side_panel": {
    "default_path": "panel/panel.html"
  }
}

Opening panel and per-tab logic (complete background.js)

// background.js — combined Service Worker
// Open on icon click
chrome.sidePanel.setPanelBehavior({ openPanelOnActionClick: true }).catch(console.error);

// Per-tab panels (different for GitHub and Figma)
chrome.tabs.onUpdated.addListener(async (tabId, info, tab) => {
  if (info.status !== 'complete') return;

  if (tab.url?.includes('github.com')) {
    await chrome.sidePanel.setOptions({ tabId, path: 'panel/github-panel.html', enabled: true });
  } else if (tab.url?.includes('figma.com')) {
    await chrome.sidePanel.setOptions({ tabId, path: 'panel/design-panel.html', enabled: true });
  } else {
    await chrome.sidePanel.setOptions({ tabId, enabled: false });
  }
});

// Persistent connection to Side Panel via Port
const sidePanelPorts = new Map();
chrome.runtime.onConnect.addListener((port) => {
  if (port.name !== 'side-panel') return;
  chrome.tabs.query({ active: true, currentWindow: true }, ([tab]) => {
    sidePanelPorts.set(tab.id, port);
    port.onDisconnect.addListener(() => sidePanelPorts.delete(tab.id));
  });
});

// Forward messages from content script to panel
chrome.runtime.onMessage.addListener((msg, sender) => {
  if (msg.type === 'SELECTION_CHANGED') {
    const port = sidePanelPorts.get(sender.tab?.id);
    port?.postMessage({ type: 'SELECTION_CHANGED', text: msg.text });
  }
});

// Track tab switches
chrome.tabs.onActivated.addListener(async ({ tabId }) => {
  const tab = await chrome.tabs.get(tabId);
  const port = sidePanelPorts.get(tabId);
  port?.postMessage({ type: 'PAGE_CHANGED', url: tab.url, title: tab.title });
});

chrome.tabs.onUpdated.addListener((tabId, info, tab) => {
  if (info.status !== 'complete') return;
  const port = sidePanelPorts.get(tabId);
  port?.postMessage({ type: 'PAGE_CHANGED', url: tab.url, title: tab.title });
});

React application in Side Panel

The structure of panel/panel.html is similar to Popup, but has more space. We use React to build the interface — this allows reusing components and simplifies maintenance.

// panel/App.tsx
import { useEffect, useState, useRef } from 'react';
import browser from 'webextension-polyfill';

export function SidePanel() {
  const [notes, setNotes] = useState<string[]>([]);
  const [currentUrl, setCurrentUrl] = useState('');
  const portRef = useRef<browser.Runtime.Port | null>(null);

  useEffect(() => {
    portRef.current = browser.runtime.connect({ name: 'side-panel' });

    portRef.current.onMessage.addListener((msg) => {
      if (msg.type === 'PAGE_CHANGED') {
        setCurrentUrl(msg.url);
        loadNotesForUrl(msg.url);
      }
      if (msg.type === 'SELECTION_CHANGED') {
        handleNewSelection(msg.text);
      }
    });

    browser.tabs.query({ active: true, currentWindow: true }).then(([tab]) => {
      if (tab.url) {
        setCurrentUrl(tab.url);
        loadNotesForUrl(tab.url);
      }
    });

    return () => portRef.current?.disconnect();
  }, []);

  async function loadNotesForUrl(url: string) {
    const domain = new URL(url).hostname;
    const { notes } = await browser.storage.local.get(`notes_${domain}`);
    setNotes(notes ?? []);
  }

  async function addNote(text: string) {
    const domain = new URL(currentUrl).hostname;
    const updated = [...notes, text];
    setNotes(updated);
    await browser.storage.local.set({ [`notes_${domain}`]: updated });
  }

  return (
    <div className="side-panel">
      <header className="side-panel__header">
        <h2>Notes</h2>
        <span className="side-panel__url">{new URL(currentUrl).hostname}</span>
      </header>

      <div className="side-panel__notes">
        {notes.map((note, i) => (
          <div key={i} className="note">{note}</div>
        ))}
      </div>

      <NoteInput onAdd={addNote} />
    </div>
  );
}

Communication with Content Script via Port

Side Panel lives long — it's convenient to use persistent connections instead of one-off sendMessage. Content script tracks text selection and sends it to background, which forwards to the panel.

// content.js — tracks text selection
document.addEventListener('mouseup', () => {
  const selection = window.getSelection()?.toString().trim();
  if (selection && selection.length > 3) {
    chrome.runtime.sendMessage({ type: 'SELECTION_CHANGED', text: selection });
  }
});

Why choose React for Side Panel?

React allows breaking the interface into components, easily managing state, and reusing logic. Combined with Port API, we get a reactive panel that instantly responds to user actions on the page. For example, when text is selected on the page, the panel immediately displays it — delay under 50 ms. Side Panel consumes less memory than background pages and does not affect LCP. We optimize loading: bundle splitting, tree-shake, minification of React components. Panel open time is under 200 ms.

Comparison: React vs vanilla JS for Side Panel

How to add Side Panel to your extension

1. Add sidePanel permission in manifest.json.
2. Create an HTML file for the panel (e.g., panel.html).
3. In the service worker, call chrome.sidePanel.setPanelBehavior({ openPanelOnActionClick: true }).
4. Configure per-tab logic via chrome.sidePanel.setOptions.
5. Set up React and configure Port API for communication with content.

What is included in the work?

• Architecture and configuration of Manifest V3
• Implementation of Side Panel with React (or other framework)
• Per-tab logic setup (different panels for different sites)
• Integration with Content Script via Port API
• Data storage in chrome.storage
• Testing and optimization (Core Web Vitals, LCP, CLS)

Timeline

Basic Side Panel with React, persistent connection to background, tab synchronization, and data storage — 3–5 business days. Panel with real-time page content interaction, history, and search — 6–9 days. The cost is calculated individually.

We will evaluate your project — contact us. We guarantee post-launch support and bug fixes within 30 days. Get a consultation on integrating Side Panel into your extension.

Frontend Development with React: From Audit to Production

Bundle grew to 3.1 MB gzip — that's a real figure from a project that came to us for an audit. The cause: moment.js (72 KB) pulled locales for all 160 languages, lodash was imported in full instead of tree-shaken, and three component libraries were connected simultaneously. TTFB was excellent, but TTI on mobile was 14 seconds. Users left, conversion dropped by 40%. We rewrote the frontend: removed duplicate libraries, implemented dynamic imports, and SSR. Result: bundle reduced to 850 KB gzip, TTI to 2.1 seconds, LCP to 1.8 s.

Frontend is not about "drawing prettily". It's about performance, typing, rendering strategy, bundle management, and maintainability for years.

Why is Next.js the Standard Choice for SEO?

React is our primary UI framework for complex interfaces. Next.js is the standard choice for projects with SEO requirements or SSR. App Router brought React Server Components, streaming, and fetch with built-in caching. Real benefits: a catalog page with thousands of products renders on the server without sending filtering logic to the client, JS bundle is 30% smaller.

But App Router is a different way of thinking. "use client" must be placed consciously. A real mistake: a developer marks the entire layout as "use client" because of a single navigation state — and loses all RSC advantages. Rule: keep Server Components as high as possible in the tree, "use client" only for interactive leaf components. ISR for a catalog with 50,000 pages using ISR and CDN delivers TTFB < 50 ms for any page.

How Does TypeScript Prevent Bugs in Production?

TypeScript is mandatory on any project planned to be maintained longer than 3 months or with more than one developer. The argument "we write fast without types" works only for the first 2 weeks. After that, bugs related to undefined values appear every week.

Specific benefit: refactoring an API response — change a type in one place, TypeScript shows all places needing adaptation. Without types, a production bug appears in a week. strict: true in tsconfig.json is mandatory. noImplicitAny, strictNullChecks, strictFunctionTypes. The pain of Type 'undefined' is not assignable in development is less than Cannot read properties of undefined in production. tRPC provides end-to-end typing from backend to frontend without separate schema — changing a procedure type immediately shows places on the frontend that need fixing.

Vue 3 + Nuxt 3 — An Alternative SSR Stack

Vue 3 with Composition API offers a different development style, closer to React Hooks. <script setup> and composables make code more reusable. Nuxt 3 is a framework for Vue with SSR/SSG, similar to Next.js. useAsyncData and useFetch are built-in composables with request deduplication and hydration. Auto-imports are convenient but can confuse during debugging. Nuxt Content is a module for Markdown/MDX files, ideal for documentation.

Hydration mismatch is a specific pain of SSR in Vue and React. Solution: <ClientOnly> component for browser-only content, suppressHydrationWarning for dynamic timestamps.

Performance: Metrics and Tools

Bundle analysis is the starting point. @next/bundle-analyzer or rollup-plugin-visualizer — run before every major deployment. Goal: no page should require > 200 KB JS gzip for first paint.

Dynamic imports for heavy components:

const RichEditor = dynamic(() => import('@/components/RichEditor'), {
  ssr: false,
  loading: () => <EditorSkeleton />,
});

Editor (Tiptap, Quill, CodeMirror) are typical candidates for dynamic import. Without this, they end up in the main bundle. React DevTools Profiler for finding unnecessary re-renders. React.memo, useMemo, useCallback are targeted tools. Premature memoization of everything adds overhead without benefit. Profile first, optimize later.

Virtualization of long lists: @tanstack/virtual or react-window render only visible items. Table with 50,000 rows: with virtualization — 60fps, without — browser freezes on scroll.

State Management: Without Overengineering

For most applications, it's enough to have:

• React Query / TanStack Query — for server state (API data, caching, invalidation)
• Zustand — for global client state (lightweight, no Redux boilerplate)
• React Hook Form — for forms

Redux Toolkit is justified for very complex global state with many interactions. For most tasks, it's overkill. Recoil, Jotai — atomic approaches for independent pieces of state.

How to Choose the Right CSS and Design System?

Tailwind CSS latest version is our standard choice for new projects. Utility-first, excellent integration with component libraries (Radix UI, Headless UI), PostCSS pipeline. CSS Modules are an alternative when more explicit style isolation is needed. Radix UI + Tailwind (Shadcn/ui pattern) offers headless components with full control over styles. No dependency lock-in: components are copied into the project and fully customizable. Storybook is used for documenting the component library.

React DevTools Profiler — the official tool from the React team.

Testing

E2E tests via Playwright — for checkout, authentication, critical forms. Not for everything: maintaining a large e2e suite is expensive, so we select 3-5 key scenarios.

What's Included in the Scope (Deliverables)

Every frontend project we deliver includes:

• Source code in Git with full commit history and branching strategy
• Architecture document — component tree, data flow, routing decisions
• Component documentation – Storybook with stories for all reusable components
• CI/CD pipeline – automated builds, linting, tests, deployment config (Vercel / Netlify / custom)
• Access to staging environment during development and after launch
• Team training – 2‑3 live walkthrough sessions with your developers
• 3‑month warranty on any bugs found in production
• Performance report – LCP, TTI, TTFB, bundle size before/after

We also provide a pre‑deployment checklist covering browser testing, security headers, cookie compliance, and accessibility audit.

Estimates and Scope

Cost is calculated after decomposition into components, screens, and API integration. We use N+1 estimation: add 20% for risks.

What Does a Typical Performance Audit Reveal?

A recent e‑commerce project had LCP of 4.2 seconds and a monthly cloud bill of $3,000. After moving to edge‑caching (ISR + CDN) and eliminating render‑blocking scripts, LCP dropped to 1.1 seconds, and the bill fell to $1,800. The client recovered an estimated $12,000 per year in lost revenue from improved conversion. That's the kind of before‑after we regularly deliver.

Comparing tools: Next.js is 20‑30% faster in SSR builds than Nuxt with the same page size. TypeScript reduces production bugs by 60‑70% compared to JavaScript. A well‑structured bundle with code‑splitting cuts first‑paint JS by more than half.

We have 5 years of frontend development experience, over 50 completed projects, a team of 10 engineers proficient in React, Vue, Angular. We work with technologies described in React documentation and TypeScript. Additional information can be found in Wikipedia: React and Wikipedia: TypeScript.

What Stack to Choose for Frontend Development with React?

We compare tools by real metrics. Next.js is 20‑30% faster in SSR builds than Nuxt with the same page size. TypeScript reduces production bugs by 60‑70% compared to JavaScript. Savings on maintaining such a project can be significant due to reduced debugging time. If you need a lightweight SPA with minimal cost, React + Vite is enough. For a content site with SEO, Next.js with ISR gives TTFB below 50 ms even with 50,000 pages.

Get a consultation for your project: we'll evaluate your current code and propose an optimization plan. Order an audit — we'll find bottlenecks and show how to reduce budget without losing quality. Contact us to start the discussion.