progressive-web-app

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English

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Translation

Chinese

Progressive Web Apps (PWAs)

Progressive Web Apps（PWA）

Overview

概述

A Progressive Web App is a web application that uses modern browser capabilities to deliver a fast, reliable, and installable experience — even on unreliable networks. The three required pillars are:

HTTPS — Required in production for service workers to register (localhost is exempt for development).
Web App Manifest (
```
manifest.json
```
) — Makes the app installable and defines its appearance on device home screens.
Service Worker (
```
sw.js
```
) — A background script that intercepts network requests, manages caches, and enables offline functionality.

渐进式Web应用（PWA）是一种利用现代浏览器功能的Web应用，可提供快速、可靠且可安装的体验——即使在网络不稳定的环境下也能正常使用。其三大核心要素为：

HTTPS —— 生产环境下注册service worker必须使用HTTPS（开发环境下localhost除外）。
Web App Manifest（
```
manifest.json
```
）—— 让应用可安装，并定义其在设备主屏幕上的显示样式。
Service Worker（
```
sw.js
```
）—— 一个后台脚本，用于拦截网络请求、管理缓存并实现离线功能。

When to Use This Skill

何时使用此技能

Use when the user wants their web app to work offline or on unreliable networks.
Use when building a mobile-first web project where users should be able to install the app to their home screen.
Use when the user asks about caching strategies, service workers, or improving web app performance and resilience.
Use when the user mentions Workbox, web app manifests, background sync, or push notifications for the web.
Use when the user asks "can my website be installed like an app?" or "how do I make my site work offline?" — even if they don't use the word PWA.

当用户希望其Web应用支持离线使用或在网络不稳定的环境下运行时。
当构建移动端优先的Web项目，且希望用户能够将应用安装到主屏幕时。
当用户询问缓存策略、service worker，或希望提升Web应用的性能和韧性时。
当用户提及Workbox、Web App Manifest、后台同步或Web推送通知时。
当用户询问“我的网站能否像应用一样安装？”或“如何让我的网站支持离线使用？”时——即使他们没有提到PWA这个词。

Deliverables Checklist

交付物检查清单

Every PWA implementation must include these files at minimum:

```
index.html
```
— Links manifest, registers service worker
```
manifest.json
```
— Full app metadata and icon set
```
sw.js
```
— Service worker with install, activate, and fetch handlers
```
app.js
```
— Main app logic with SW registration and install prompt handling
```
offline.html
```
— Fallback page shown when navigation fails offline (required — missing file will cause install to fail)

每个PWA实现至少必须包含以下文件：

```
index.html
```
—— 关联manifest，注册service worker
```
manifest.json
```
—— 完整的应用元数据和图标集
```
sw.js
```
—— 包含install、activate和fetch处理器的service worker
```
app.js
```
—— 包含SW注册和安装提示处理的主应用逻辑
```
offline.html
```
—— 离线导航失败时显示的备用页面（必填——缺少此文件会导致安装失败）

Step 1: Web App Manifest (

manifest.json

)

步骤1：Web App Manifest（

manifest.json

）

Defines how the app appears when installed. Must be linked from

<head>

via

<link rel="manifest">

json

{
  "name": "My Awesome PWA",
  "short_name": "MyPWA",
  "description": "A fast, offline-capable Progressive Web App.",
  "start_url": "/",
  "scope": "/",
  "display": "standalone",
  "orientation": "portrait-primary",
  "background_color": "#ffffff",
  "theme_color": "#0055ff",
  "icons": [
    {
      "src": "/assets/icons/icon-192x192.png",
      "sizes": "192x192",
      "type": "image/png",
      "purpose": "any maskable"
    },
    {
      "src": "/assets/icons/icon-512x512.png",
      "sizes": "512x512",
      "type": "image/png",
      "purpose": "any maskable"
    }
  ],
  "screenshots": [
    {
      "src": "/assets/screenshots/desktop.png",
      "sizes": "1280x720",
      "type": "image/png",
      "form_factor": "wide"
    }
  ]
}

Key fields:

```
display
```
:
```
standalone
```
hides browser UI;
```
minimal-ui
```
shows minimal controls;
```
browser
```
is standard tab.
```
purpose: "maskable"
```
on icons enables adaptive icons on Android (safe zone matters — keep content in center 80%).
```
screenshots
```
is optional but required for Chrome's enhanced install dialog on desktop.

定义应用安装后的显示样式。必须通过

<head>

中的

<link rel="manifest">

进行关联。

json

{
  "name": "My Awesome PWA",
  "short_name": "MyPWA",
  "description": "A fast, offline-capable Progressive Web App.",
  "start_url": "/",
  "scope": "/",
  "display": "standalone",
  "orientation": "portrait-primary",
  "background_color": "#ffffff",
  "theme_color": "#0055ff",
  "icons": [
    {
      "src": "/assets/icons/icon-192x192.png",
      "sizes": "192x192",
      "type": "image/png",
      "purpose": "any maskable"
    },
    {
      "src": "/assets/icons/icon-512x512.png",
      "sizes": "512x512",
      "type": "image/png",
      "purpose": "any maskable"
    }
  ],
  "screenshots": [
    {
      "src": "/assets/screenshots/desktop.png",
      "sizes": "1280x720",
      "type": "image/png",
      "form_factor": "wide"
    }
  ]
}

关键字段：

```
display
```
：
```
standalone
```
会隐藏浏览器UI；
```
minimal-ui
```
显示极简控制栏；
```
browser
```
为标准标签页模式。
图标上的
```
purpose: "maskable"
```
支持Android自适应图标（注意安全区域——内容需保持在中心80%范围内）。
```
screenshots
```
为可选字段，但桌面端Chrome的增强安装对话框需要此字段。

Step 2: HTML Shell (

index.html

)

步骤2：HTML外壳（

index.html

）

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>My Awesome PWA</title>

  <!-- PWA manifest -->
  <link rel="manifest" href="/manifest.json">

  <!-- Theme color for browser chrome -->
  <meta name="theme-color" content="#0055ff">

  <!-- iOS-specific (Safari doesn't fully use manifest) -->
  <meta name="apple-mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-status-bar-style" content="default">
  <meta name="apple-mobile-web-app-title" content="MyPWA">
  <link rel="apple-touch-icon" href="/assets/icons/icon-192x192.png">

  <link rel="stylesheet" href="/styles.css">
</head>
<body>
  <div id="app">
    <header><h1>My PWA</h1></header>
    <main id="content">Loading...</main>
    <!-- Optional: install button, hidden by default -->
    <button id="install-btn" hidden>Install App</button>
  </div>
  <script src="/app.js"></script>
</body>
</html>

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>My Awesome PWA</title>

  <!-- PWA manifest -->
  <link rel="manifest" href="/manifest.json">

  <!-- 浏览器主题色 -->
  <meta name="theme-color" content="#0055ff">

  <!-- iOS专属配置（Safari未完全支持manifest） -->
  <meta name="apple-mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-status-bar-style" content="default">
  <meta name="apple-mobile-web-app-title" content="MyPWA">
  <link rel="apple-touch-icon" href="/assets/icons/icon-192x192.png">

  <link rel="stylesheet" href="/styles.css">
</head>
<body>
  <div id="app">
    <header><h1>My PWA</h1></header>
    <main id="content">Loading...</main>
    <!-- 可选：安装按钮，默认隐藏 -->
    <button id="install-btn" hidden>Install App</button>
  </div>
  <script src="/app.js"></script>
</body>
</html>

Step 3: Service Worker Registration & Install Prompt (

app.js

)

步骤3：Service Worker注册与安装提示（

app.js

）

javascript

// ─── Service Worker Registration ───────────────────────────────────────────
if ('serviceWorker' in navigator) {
  window.addEventListener('load', async () => {
    try {
      const registration = await navigator.serviceWorker.register('/sw.js');
      console.log('[App] SW registered, scope:', registration.scope);
    } catch (err) {
      console.error('[App] SW registration failed:', err);
    }
  });
}

// ─── Install Prompt (Add to Home Screen) ───────────────────────────────────
let deferredPrompt;
const installBtn = document.getElementById('install-btn'); // may be null if omitted

// Capture the browser's install prompt — it fires before the browser's own UI
window.addEventListener('beforeinstallprompt', (e) => {
  e.preventDefault(); // Stop automatic mini-infobar on mobile
  deferredPrompt = e;
  if (installBtn) installBtn.hidden = false; // Show your custom install button
});

if (installBtn) {
  installBtn.addEventListener('click', async () => {
    if (!deferredPrompt) return;
    deferredPrompt.prompt();
    const { outcome } = await deferredPrompt.userChoice;
    console.log('[App] Install outcome:', outcome);
    deferredPrompt = null;
    installBtn.hidden = true;
  });
}
// Fires when the app is installed (via browser or your button)
window.addEventListener('appinstalled', () => {
  console.log('[App] PWA installed successfully');
  installBtn.hidden = true;
});

javascript

// ─── Service Worker 注册 ───────────────────────────────────────────
if ('serviceWorker' in navigator) {
  window.addEventListener('load', async () => {
    try {
      const registration = await navigator.serviceWorker.register('/sw.js');
      console.log('[App] SW registered, scope:', registration.scope);
    } catch (err) {
      console.error('[App] SW registration failed:', err);
    }
  });
}

// ─── 安装提示（添加到主屏幕） ───────────────────────────────────
let deferredPrompt;
const installBtn = document.getElementById('install-btn'); // 若省略则可能为null

// 捕获浏览器的安装提示——该事件在浏览器自身UI弹出前触发
window.addEventListener('beforeinstallprompt', (e) => {
  e.preventDefault(); // 阻止移动端自动显示迷你信息栏
  deferredPrompt = e;
  if (installBtn) installBtn.hidden = false; // 显示自定义安装按钮
});

if (installBtn) {
  installBtn.addEventListener('click', async () => {
    if (!deferredPrompt) return;
    deferredPrompt.prompt();
    const { outcome } = await deferredPrompt.userChoice;
    console.log('[App] Install outcome:', outcome);
    deferredPrompt = null;
    installBtn.hidden = true;
  });
}
// 应用安装完成时触发（通过浏览器或自定义按钮安装）
window.addEventListener('appinstalled', () => {
  console.log('[App] PWA installed successfully');
  installBtn.hidden = true;
});

Step 4: Service Worker (

sw.js

)

步骤4：Service Worker（

sw.js

）

Cache Versioning (critical — always increment on deploy)

缓存版本控制（至关重要——部署时务必递增版本号）

javascript

const CACHE_VERSION = 'v1';
const STATIC_CACHE = `static-${CACHE_VERSION}`;
const DYNAMIC_CACHE = `dynamic-${CACHE_VERSION}`;

// Files to pre-cache during install (the "App Shell")
const APP_SHELL = [
  '/',
  '/index.html',
  '/styles.css',
  '/app.js',
  '/assets/icons/icon-192x192.png',
  '/offline.html', // Fallback page shown when network is unavailable
];

javascript

const CACHE_VERSION = 'v1';
const STATIC_CACHE = `static-${CACHE_VERSION}`;
const DYNAMIC_CACHE = `dynamic-${CACHE_VERSION}`;

// 安装期间预缓存的文件（“应用外壳”）
const APP_SHELL = [
  '/',
  '/index.html',
  '/styles.css',
  '/app.js',
  '/assets/icons/icon-192x192.png',
  '/offline.html', // 网络不可用时显示的备用页面
];

Install — Pre-cache the App Shell

安装——预缓存应用外壳

javascript

self.addEventListener('install', (event) => {
  console.log('[SW] Installing...');
  event.waitUntil(
    caches.open(STATIC_CACHE).then((cache) => {
      console.log('[SW] Pre-caching app shell');
      return cache.addAll(APP_SHELL);
    })
  );
  // Activate immediately without waiting for old SW to die
  self.skipWaiting();
});

javascript

self.addEventListener('install', (event) => {
  console.log('[SW] Installing...');
  event.waitUntil(
    caches.open(STATIC_CACHE).then((cache) => {
      console.log('[SW] Pre-caching app shell');
      return cache.addAll(APP_SHELL);
    })
  );
  // 立即激活，无需等待旧SW终止
  self.skipWaiting();
});

Activate — Clean Up Old Caches

激活——清理旧缓存

javascript

self.addEventListener('activate', (event) => {
  console.log('[SW] Activating...');
  event.waitUntil(
    caches.keys().then((cacheNames) => {
      return Promise.all(
        cacheNames
          .filter((name) => name !== STATIC_CACHE && name !== DYNAMIC_CACHE)
          .map((name) => {
            console.log('[SW] Deleting old cache:', name);
            return caches.delete(name);
          })
      );
    })
  );
  // Take control of all pages immediately
  self.clients.claim();
});

javascript

self.addEventListener('activate', (event) => {
  console.log('[SW] Activating...');
  event.waitUntil(
    caches.keys().then((cacheNames) => {
      return Promise.all(
        cacheNames
          .filter((name) => name !== STATIC_CACHE && name !== DYNAMIC_CACHE)
          .map((name) => {
            console.log('[SW] Deleting old cache:', name);
            return caches.delete(name);
          })
      );
    })
  );
  // 立即接管所有页面
  self.clients.claim();
});

Fetch — Caching Strategies

Fetch——缓存策略

Choose the right strategy per resource type:

javascript

self.addEventListener('fetch', (event) => {
  const { request } = event;
  const url = new URL(request.url);

  // Only handle GET requests from our own origin
  if (request.method !== 'GET' || url.origin !== location.origin) return;

  // Strategy A: Cache-First (for static assets — fast, tolerates stale)
  if (url.pathname.match(/\.(css|js|png|jpg|svg|woff2)$/)) {
    event.respondWith(cacheFirst(request));
    return;
  }

  // Strategy B: Network-First (for HTML pages — fresh, falls back to cache)
  if (request.headers.get('Accept')?.includes('text/html')) {
    event.respondWith(networkFirst(request));
    return;
  }

  // Strategy C: Stale-While-Revalidate (for API data — fast and eventually fresh)
  if (url.pathname.startsWith('/api/')) {
    event.respondWith(staleWhileRevalidate(request));
    return;
  }
});

// ─── Strategy Implementations ──────────────────────────────────────────────

async function cacheFirst(request) {
  const cached = await caches.match(request);
  if (cached) return cached;
  try {
    const response = await fetch(request);
    const cache = await caches.open(STATIC_CACHE);
    cache.put(request, response.clone());
    return response;
  } catch {
    // Nothing useful to fall back to for assets
    return new Response('Asset unavailable offline', { status: 503 });
  }
}

async function networkFirst(request) {
  try {
    const response = await fetch(request);
    const cache = await caches.open(DYNAMIC_CACHE);
    cache.put(request, response.clone());
    return response;
  } catch {
    const cached = await caches.match(request);
    return cached || caches.match('/offline.html');
  }
}

async function staleWhileRevalidate(request) {
  const cache = await caches.open(DYNAMIC_CACHE);
  const cached = await cache.match(request);
  const fetchPromise = fetch(request).then((response) => {
    cache.put(request, response.clone());
    return response;
  });
  return cached || fetchPromise;
}

根据资源类型选择合适的策略：

javascript

self.addEventListener('fetch', (event) => {
  const { request } = event;
  const url = new URL(request.url);

  // 仅处理同源的GET请求
  if (request.method !== 'GET' || url.origin !== location.origin) return;

  // 策略A：缓存优先（适用于静态资源——速度快，可接受过期内容）
  if (url.pathname.match(/\.(css|js|png|jpg|svg|woff2)$/)) {
    event.respondWith(cacheFirst(request));
    return;
  }

  // 策略B：网络优先（适用于HTML页面——内容新鲜，缓存作为备用）
  if (request.headers.get('Accept')?.includes('text/html')) {
    event.respondWith(networkFirst(request));
    return;
  }

  // 策略C：缓存回源（适用于API数据——速度快且最终会更新为最新内容）
  if (url.pathname.startsWith('/api/')) {
    event.respondWith(staleWhileRevalidate(request));
    return;
  }
});

// ─── 策略实现 ──────────────────────────────────────────────

async function cacheFirst(request) {
  const cached = await caches.match(request);
  if (cached) return cached;
  try {
    const response = await fetch(request);
    const cache = await caches.open(STATIC_CACHE);
    cache.put(request, response.clone());
    return response;
  } catch {
    // 资源离线时无可用备用内容
    return new Response('Asset unavailable offline', { status: 503 });
  }
}

async function networkFirst(request) {
  try {
    const response = await fetch(request);
    const cache = await caches.open(DYNAMIC_CACHE);
    cache.put(request, response.clone());
    return response;
  } catch {
    const cached = await caches.match(request);
    return cached || caches.match('/offline.html');
  }
}

async function staleWhileRevalidate(request) {
  const cache = await caches.open(DYNAMIC_CACHE);
  const cached = await cache.match(request);
  const fetchPromise = fetch(request).then((response) => {
    cache.put(request, response.clone());
    return response;
  });
  return cached || fetchPromise;
}

Edge Cases & Platform Notes

边缘情况与平台说明

iOS / Safari Quirks

iOS / Safari 特性

Safari supports manifests and service workers but does not support
beforeinstallprompt
— users must install via the Share → "Add to Home Screen" menu manually.
Use the
```
apple-mobile-web-app-*
```
meta tags (shown in
```
index.html
```
above) for proper iOS integration.
Safari may clear service worker caches after ~7 days of inactivity (Intelligent Tracking Prevention).

Safari支持manifest和service worker，但不支持
beforeinstallprompt
——用户必须通过分享→“添加到主屏幕”菜单手动安装。
使用
```
apple-mobile-web-app-*
```
元标签（如上述
```
index.html
```
中所示）实现iOS的正确集成。
Safari可能会在应用闲置约7天后清除service worker缓存（智能跟踪预防机制）。

HTTPS Requirement

HTTPS要求

Service workers only register on
```
https://
```
origins.
```
http://localhost
```
is the only exception for development.
Use a tool like
```
mkcert
```
or
```
ngrok
```
if you need HTTPS locally with a custom hostname.

Service worker仅能在
```
https://
```
源上注册。开发环境下
```
http://localhost
```
是唯一例外。
如果需要在本地自定义主机名上使用HTTPS，可以使用
```
mkcert
```
或
```
ngrok
```
等工具。

Cache-Busting on Deploy

部署时的缓存更新

Always increment
```
CACHE_VERSION
```
in
```
sw.js
```
when deploying new assets. This ensures activate clears old caches and users get fresh files.
A common pattern is to inject the version automatically via your build tool (e.g., Vite, Webpack).

部署新资源时，务必递增
```
sw.js
```
中的
```
CACHE_VERSION
```
。这样可以确保激活阶段清理旧缓存，用户获取到最新文件。
常见做法是通过构建工具（如Vite、Webpack）自动注入版本号。

Opaque Responses (cross-origin requests)

不透明响应（跨域请求）

Requests to external origins (e.g., CDN fonts, third-party APIs) return "opaque" responses that cannot be inspected. Cache them with caution — a failed opaque response still gets a
```
200
```
status.
Prefer
```
staleWhileRevalidate
```
for cross-origin resources, or use a library like Workbox which handles this safely.

对外部源的请求（如CDN字体、第三方API）会返回“不透明”响应，无法被检查。缓存此类响应时需谨慎——失败的不透明响应仍会返回
```
200
```
状态码。
对于跨域资源，优先使用
```
staleWhileRevalidate
```
策略，或使用Workbox等库来安全处理此类情况。

Workbox (Optional: Production Shortcut)

Workbox（可选：生产环境快捷工具）

For production apps, consider Workbox (Google's PWA library) instead of hand-rolling strategies. It handles edge cases, cache expiry, and versioning automatically.

javascript

// With Workbox (via CDN for simplicity — use npm + bundler in production)
importScripts('https://storage.googleapis.com/workbox-cdn/releases/7.0.0/workbox-sw.js');

const { registerRoute } = workbox.routing;
const { CacheFirst, NetworkFirst, StaleWhileRevalidate } = workbox.strategies;
const { precacheAndRoute } = workbox.precaching;

precacheAndRoute(self.__WB_MANIFEST || []); // Injected by build plugin

registerRoute(({ request }) => request.destination === 'image', new CacheFirst());
registerRoute(({ request }) => request.mode === 'navigate', new NetworkFirst());
registerRoute(({ request }) => request.destination === 'script', new StaleWhileRevalidate());

对于生产环境应用，考虑使用Workbox（谷歌的PWA库）替代手动编写策略。它会自动处理边缘情况、缓存过期和版本控制。

javascript

// 使用Workbox（为简化使用CDN——生产环境建议使用npm + 打包工具）
importScripts('https://storage.googleapis.com/workbox-cdn/releases/7.0.0/workbox-sw.js');

const { registerRoute } = workbox.routing;
const { CacheFirst, NetworkFirst, StaleWhileRevalidate } = workbox.strategies;
const { precacheAndRoute } = workbox.precaching;

precacheAndRoute(self.__WB_MANIFEST || []); // 由构建插件注入

registerRoute(({ request }) => request.destination === 'image', new CacheFirst());
registerRoute(({ request }) => request.mode === 'navigate', new NetworkFirst());
registerRoute(({ request }) => request.destination === 'script', new StaleWhileRevalidate());

Checklist Before Shipping

上线前检查清单

Site is served over HTTPS

manifest.json

has

name

short_name

start_url

display

icons

(192 + 512)

Icons have
```
purpose: "any maskable"
```
```
sw.js
```
registers without errors in DevTools → Application → Service Workers
App shell loads from cache when network is throttled to "Offline" in DevTools
```
offline.html
```
fallback is cached and served when navigation fails offline
Lighthouse PWA audit passes (Chrome DevTools → Lighthouse tab)
Tested on iOS Safari (manual install flow) and Android Chrome (install prompt)

网站通过HTTPS提供服务
```
manifest.json
```
包含
```
name
```
、
```
short_name
```
、
```
start_url
```
、
```
display
```
、图标（192×192和512×512）
图标设置了
```
purpose: "any maskable"
```
```
sw.js
```
在DevTools→Application→Service Workers中注册无错误
当网络被限制为“离线”时，应用外壳可从缓存加载
```
offline.html
```
备用页面已被缓存，且在离线导航失败时正常显示
Lighthouse PWA审核通过（Chrome DevTools→Lighthouse标签）
已在iOS Safari（手动安装流程）和Android Chrome（安装提示）上进行测试

progressive-web-app

Original

Translation

Progressive Web Apps (PWAs)

Progressive Web Apps（PWA）

Overview

概述

When to Use This Skill

何时使用此技能

Deliverables Checklist

交付物检查清单

Step 1: Web App Manifest (manifest.json)

步骤1：Web App Manifest（manifest.json）

Step 2: HTML Shell (index.html)

步骤2：HTML外壳（index.html）

Step 3: Service Worker Registration & Install Prompt (app.js)

步骤3：Service Worker注册与安装提示（app.js）

Step 4: Service Worker (sw.js)

步骤4：Service Worker（sw.js）

Cache Versioning (critical — always increment on deploy)

缓存版本控制（至关重要——部署时务必递增版本号）

Install — Pre-cache the App Shell

安装——预缓存应用外壳

Activate — Clean Up Old Caches

激活——清理旧缓存

Fetch — Caching Strategies

Fetch——缓存策略

Edge Cases & Platform Notes

边缘情况与平台说明

iOS / Safari Quirks

iOS / Safari 特性

HTTPS Requirement

HTTPS要求

Cache-Busting on Deploy

部署时的缓存更新

Opaque Responses (cross-origin requests)

不透明响应（跨域请求）

Workbox (Optional: Production Shortcut)

Workbox（可选：生产环境快捷工具）

Checklist Before Shipping

上线前检查清单

Step 1: Web App Manifest (
`manifest.json`
)

步骤1：Web App Manifest（
`manifest.json`
）

Step 2: HTML Shell (
`index.html`
)

步骤2：HTML外壳（
`index.html`
）

Step 3: Service Worker Registration & Install Prompt (
`app.js`
)

步骤3：Service Worker注册与安装提示（
`app.js`
）

Step 4: Service Worker (
`sw.js`
)

步骤4：Service Worker（
`sw.js`
）