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February 11, 2022 05:14
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use indexdb on browser to cache image files ( map tile image in the example)
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| <!-- working example https://jsfiddle.net/qz9g53bt/2/ --> | |
| <!-- from https://github.com/allartk/leaflet.offline --> | |
| <!DOCTYPE html> | |
| <html lang="en"> | |
| <head> | |
| <meta charset="UTF-8" /> | |
| <meta http-equiv="X-UA-Compatible" content="IE=edge" /> | |
| <meta name="viewport" content="width=device-width, initial-scale=1.0" /> | |
| <script src="https://unpkg.com/[email protected]/build/iife/index-min.js"></script> | |
| <title>Document</title> | |
| </head> | |
| <body> | |
| <div> | |
| <button id="clean">clean idb cache</button> | |
| </div> | |
| <div id="msgs" /> | |
| <div id="root" /> | |
| <script type="module"> | |
| const { openDB, deleteDB } = idb; | |
| main(); | |
| function addMsg(msg = '') { | |
| document.getElementById('msgs').innerHTML += msg; | |
| console.log(`$ addMsg`, msg); | |
| } | |
| async function main() { | |
| const tileStoreName = 'tileStorage'; | |
| const urlTemplateIndex = 'urlTemplate'; | |
| const db = await openDB('leaflet.offline', 2, { | |
| upgrade(db, oldVersion) { | |
| deleteDB('leaflet_offline'); | |
| deleteDB('leaflet_offline_areas'); | |
| if (oldVersion < 1) { | |
| const tileStore = db.createObjectStore(tileStoreName, { | |
| keyPath: 'key', | |
| }); | |
| tileStore.createIndex(urlTemplateIndex, 'urlTemplate'); | |
| tileStore.createIndex('z', 'z'); | |
| } | |
| }, | |
| }); | |
| const imgEle = document.createElement('img'); | |
| const cacheKey = 'cacheImage'; | |
| const cacheImage = await db.get(tileStoreName, cacheKey); | |
| if (cacheImage === undefined) { | |
| fetch('https://tile.openstreetmap.org/10/836/446.png').then( | |
| async (res) => { | |
| const b = await res.blob(); | |
| console.log(`$ b`, b); | |
| await db.put(tileStoreName, { | |
| key: cacheKey, | |
| blob: b, | |
| }); | |
| const url = URL.createObjectURL(b); | |
| imgEle.src = url; | |
| addMsg('image added from fetch request'); | |
| } | |
| ); | |
| } else { | |
| console.log(`$ cacheImage.blob`, cacheImage.blob); | |
| const url = URL.createObjectURL(cacheImage.blob); | |
| imgEle.src = url; | |
| addMsg('image added from idb cache'); | |
| } | |
| document.getElementById('root').appendChild(imgEle); | |
| document.getElementById('clean').onclick = () => { | |
| db.clear(tileStoreName, cacheKey); | |
| }; | |
| } | |
| </script> | |
| </body> | |
| </html> |
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