一、service worker是什么？
二、service worker的作用？
1.离线缓存（重点）2.消息推送（重点）3.后台数据同步4.响应来自其它源的资源请求，5.集中接收计算成本高的数据更新，比如地理位置和陀螺仪信息，这样多个页面就可以利6.用同一组数据7.在客户端进行CoffeeScript，LESS，CJS/AMD等模块编译和依赖管理（用于开发目的）8.后台服务钩子9.自定义模板用于特定URL模式10.性能增强，比如预取用户可能需要的资源，比如相册中的后面数张图片
三、service worker的局限
1、https: Service Worker必须是https协议的，但本地环境下http://localhost或者http://127.0.0.1也可以的。2、浏览器兼容性：
四、service worker的调试
1、chrome://serviceworker-internals
2、网页中Application五、service worker的生命周期
Service Worker生命周期的反应： installing → installed → activating → activated'install'用来缓存文件，'activate'用来缓存更新
六、service worker的用法
1、html中
if ('serviceWorker' in navigator) {
// 开始注册service workers
navigator.serviceWorker.register('./sw-demo-cache.js', {
scope: './'
}).then(function (registration) {
console.log('注册成功');
var serviceWorker;
if (registration.installing) {
serviceWorker = registration.installing;
console.log('安装installing');
} else if (registration.waiting) {
serviceWorker = registration.waiting;
console.log('等待waiting');
} else if (registration.active) {
serviceWorker = registration.active;
console.log('激活active');
}
console.log('=>serviceWorker:', serviceWorker);
if (serviceWorker) {
console.log(serviceWorker.state);
serviceWorker.addEventListener('statechange', function (e) {
console.log(' 状态变化为', e.target.state);
});
// 创建信道
var channel = new MessageChannel();
// port1留给自己
channel.port1.onmessage = e => {
console.log('main thread receive message...');
console.log(e);
}
console.log('给对方', window.RES_MAP);
// port2给对方
serviceWorker.postMessage(window.RES_MAP, [channel.port1]);
serviceWorker.addEventListener('statechange', function (e) {
// logState(e.target.state);
});
}
}).catch(function (error) {
console.log('注册没有成功');
});
} else {
console.log('不支持');
}
2、引进sw-demo-cache.js
// sw
self.addEventListener('message', ev => {
console.log('sw receive message..');
console.log(ev);
fileMap = ev.data.RES_MAP;
var arr1 = [].slice.call(fileMap); // ['a', 'b', 'c']
// 取main thread传来的port2
ev.ports[0].postMessage('Hi, hello too');
});
// var fs = require('fs');
// console.log(fs);
// 缓存
self.addEventListener('install', function(event) {
event.waitUntil(
caches.open(VERSION).then(function(cache) {
return cache.addAll([
'./index.html',
]);
})
);
});
// 缓存更新
self.addEventListener('activate', function(event) {
console.log('two now ready to handle fetches!');
event.waitUntil(
caches.keys().then(function(cacheNames) {
return Promise.all(
cacheNames.map(function(cacheName) {
console.log('cacheName:', cacheName);
// 如果当前版本和缓存版本不一致
if (cacheName !== VERSION) {
return caches.delete(cacheName);
}
})
);
})
);
});
// 捕获请求并返回缓存数据
self.addEventListener('fetch', function (event) {
try{
event.respondWith(
caches.match(event.request).then(function(res){
if(res){
return res;
}
requestBackend(event);
})
)
} catch {
console.log(event);
}
});
function requestBackend(event){
var url = event.request.clone();
return fetch(url).then(function(res){
//if not a valid response send the error
if(!res || res.status !== 200 || res.type !== 'basic'){
return res;
}
var response = res.clone();
console.log('VERSION:', VERSION);
caches.open(VERSION).then(function(cache){
cache.put(event.request, response);
});
return res;
})
}
3、webapck中获取文件目录引入第三个模块glob，递归获取打包后的文件目录
exports.resMap = function () {
var entryFiles = glob.sync(PAGE_PATH + '/*/*.js')
var map = {}
entryFiles.forEach((filePath) => {
var filename = filePath.substring(filePath.lastIndexOf('\/') + 1, filePath.lastIndexOf('.'))
map[filename] = filePath;
})
var entryFiles2 = glob.sync(PAGE_PATH2 + '/*')
var map2 = {}
findPath(entryFiles2, map2);
console.log('map2', map2);
return map2;
};
function findPath(entryFiles2, map2) {
entryFiles2.forEach(filePath => {
var filename = filePath.substring(filePath.lastIndexOf('/') + 1, filePath.lastIndexOf('.'));
if (filePath.indexOf('.') <= 0) {
let pathRes = path.resolve(__dirname, filePath);
let files = glob.sync(pathRes + '/*');
findPath(files, map2);
map2[filename] = filePath;
}
map2[filename] = filePath;
});
}
4、导出目录通过webpack的DefinePlugin插件，导出上步获取的目录5、web和service worker的通信通过postMessage实现web和service worker间的通信
// 创建信道
var channel = new MessageChannel();
// port1留给自己
channel.port1.onmessage = e => {
console.log('main thread receive message...');
console.log(e);
}
console.log('给对方', window.RES_MAP);
// port2给对方
serviceWorker.postMessage(window.RES_MAP, [channel.port1]);
serviceWorker.addEventListener('statechange', function (e) {
// logState(e.target.state);
});
// sw
self.addEventListener('message', ev => {
console.log('sw receive message..');
console.log(ev);
fileMap = ev.data.RES_MAP;
var arr1 = [].slice.call(fileMap); // ['a', 'b', 'c']
// 取main thread传来的port2
ev.ports[0].postMessage('Hi, hello too');
});
小结
1、service worker让离线缓存成为可能，offline情况下也可以访问页面。然而销毁比较困难，更新会有问题。目前只能chrome://serviceworker-internals手动销毁，还待研究。