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Service Worker for Caching Images using IndexedDB
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8"> | |
| <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> | |
| <meta name="viewport" content="width=device-width"> | |
| <title>Service worker demo</title> | |
| <!--[if lt IE 9]> | |
| <script src="//html5shiv.googlecode.com/svn/trunk/html5.js"></script> | |
| <![endif]--> | |
| <script type="text/javascript"> | |
| if ('serviceWorker' in navigator) { | |
| navigator.serviceWorker.register('sw.js', { scope: '/' }) | |
| } else { | |
| console.warn("==> Browser doesn't support Service Workers!!") | |
| } | |
| </script> | |
| </head> | |
| <body> | |
| <img src="https://as1.ftcdn.net/jpg/00/92/53/56/500_F_92535664_IvFsQeHjBzfE6sD4VHdO8u5OHUSc6yHF.jpg?cacheId=1234" alt="Image 1" /> | |
| <img src="https://thumbs.dreamstime.com/b/sample-stamp-sample-stamp-sign-icon-editable-vector-illustration-isolated-white-background-123951468.jpg?cacheId=4568" alt="Image 2" /> | |
| </body> | |
| </html> |
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| /* eslint-disable no-undef */ | |
| importScripts("/dexie.min.js") | |
| const CACHE_ID_FIELD = "cacheId" | |
| const CACHE_COUNT_LIMIT = 49 | |
| // N.B.: The below constants imply a max value of allotted file storage for caching to be (49 + 1) * 10 mb ~=500mb | |
| const CACHE_MIN_FILE_SIZE = 0 // in bytes | |
| const CACHE_MAX_FILE_SIZE = 10000000 // ~10mb in bytes | |
| const db = new Dexie("images") | |
| db.version(1).stores({ | |
| cache: "id,ts" // the indices | |
| }) | |
| function getUrlParameter(name, url) { // ref: https://davidwalsh.name/query-string-javascript | |
| // eslint-disable-next-line no-param-reassign | |
| name = name.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]") | |
| const regex = new RegExp(`[\\?&]${name}=([^&#]*)`) | |
| const results = regex.exec(url) | |
| return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " ")) | |
| } | |
| function checkCacheable(fetchRequest) { | |
| if (fetchRequest.method !== "GET" || fetchRequest.destination !== "image") return { isCacheable: false } // only images | |
| const id = getUrlParameter(CACHE_ID_FIELD, fetchRequest.url) | |
| if (id === undefined || id === null) return { isCacheable: false } | |
| return { isCacheable: true, id } | |
| } | |
| this.addEventListener("install", (event) => { | |
| console.log("sw installed....") | |
| }) | |
| this.addEventListener("fetch", async (fetchEvent) => { | |
| fetchEvent.respondWith( | |
| (async (event) => { // an async IIFE | |
| const { isCacheable, id } = checkCacheable(event.request) | |
| if (isCacheable === true) { | |
| const inCacheCnt = await db.cache.where("id").equals(id).count() | |
| if (inCacheCnt === 0) { // cache MISS | |
| const response = await fetch(event.request.url) | |
| const blob = await response.clone().blob() | |
| if (blob.size >= CACHE_MAX_FILE_SIZE || blob.size <= CACHE_MIN_FILE_SIZE) return response // don't cache too big or too small files | |
| await db.cache.put({ id, blob, ts: Date.now() }) | |
| // LRU eviction, if required (basically, when allotted file storage is near depletion): | |
| const allCnt = await db.cache.count() | |
| if (allCnt >= CACHE_COUNT_LIMIT) { | |
| const oldest = await db.cache.orderBy("ts").first() | |
| await db.cache.where("id").equals(oldest.id).delete() | |
| } | |
| return response | |
| } | |
| // cache HIT: | |
| const cached = await db.cache.get(id) | |
| await db.cache.update(id, { ts: Date.now() }) | |
| return new Response(cached.blob, { status: 200, statusText: "Cached in IndexedDB" }) | |
| } | |
| return fetch(event.request) // not cacheable url. Fallback to network. | |
| })(fetchEvent) | |
| ) | |
| }) |
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