Service Worker:当服务器上的文件发生变化时，如何更新缓存

您使用什么缓存策略?我读了离线烹饪书，最简单的策略是缓存静态内容，并忽略API调用。

这个策略看起来像这样:

1. 检查请求是否已经在缓存中
2. 如果不添加请求，响应对缓存
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3. 返回响应/gh>

如何更新缓存，如果在服务器端文件已更改?目前客户端总是得到缓存的结果。

下面是我的缓存策略代码:

// You will need this polyfill, at least on Chrome 41 and older.
importScripts("serviceworker-cache-polyfill.js");
var VERSION = 1;
var CACHES = {
    common: "common-cache" + VERSION
};
// an array of file locations we want to cache
var filesToCache = [
    "font-cache.html",
    "script.js",
];
var neededFiles = [
    "index.html"
];
var errorResponse = function() {
    return new Response([
            "<h2>Failed to get file</h2>",
            "<p>Could not retrive response from cache</p>"
        ].join("'n"),
        500
    );
};
var networkFetch = function(request) {
    return fetch(request).then(function(response) {
        caches.open(CACHES["common"]).then(function(cache) {
            return cache.put(request, response);
        });
    }).catch(function() {
        console.error("Network fetch failed");
        return errorResponse();
    });
}
this.addEventListener("install", function(evt) {
    evt.waitUntil(
        caches.open(CACHES["common"]).then(function(cache) {
            // Cache before
            cache.addAll(filesToCache);
            return cache.addAll(neededFiles);
        })
    );
});
this.addEventListener("activate", function(event) {
    var expectedCacheNames = Object.keys(CACHES).map(function(key) {
        return CACHES[key];
    });
    console.log("Activate the worker");
    // Active worker won"t be treated as activated until promise resolves successfully.
    event.waitUntil(
        caches.keys().then(function(cacheNames) {
            return Promise.all(
                cacheNames.map(function(cacheName) {
                    if (expectedCacheNames.indexOf() ===
                        -1) {
                        console.log(
                            "Deleting out of date cache:",
                            cacheName);
                        return caches.delete(cacheName);
                    }
                })
            );
        })
    );
});
self.addEventListener("fetch", function(event) {
    console.log("Handling fetch event for", event.request.url);
    event.respondWith(
        // Opens Cache objects
        caches.open(CACHES["common"]).then(function(cache) {
            return cache.match(event.request).then(function(
                response) {
                if (response) {
                    console.log("Found response in cache", response);
                    return response;
                } else {
                    return networkFetch(event.request);
                }
            }).catch(function(error) {
                // Handles exceptions that arise from match() or fetch().
                console.error(
                    "  Error in fetch handler:",
                    error);
                return errorResponse();
            });
        })
    );
});