import React from 'react' import Link, { isLocal } from './link' import { parse as urlParse } from 'url' class Messenger { constructor () { this.id = 0 this.callacks = {} this.serviceWorkerReadyCallbacks = [] this.serviceWorkerState = null navigator.serviceWorker.addEventListener('message', ({ data }) => { if (data.action !== 'REPLY') return if (this.callacks[data.replyFor]) { this.callacks[data.replyFor](data) } }) // Reset the cache always. // Sometimes, there's an already running service worker with cached requests. // If the app doesn't use any prefetch calls, `ensureInitialized` won't get // called and cleanup resources. // So, that's why we do this. this._resetCache() } send (payload, cb) { if (this.serviceWorkerState === 'REGISTERED') { this._send(payload, cb) } else { this.serviceWorkerReadyCallbacks.push(() => { this._send(payload, cb) }) } } _send (payload, cb = () => {}) { const id = this.id ++ const newPayload = { ...payload, id } this.callacks[id] = (data) => { if (data.error) { cb(data.error) } else { cb(null, data.result) } delete this.callacks[id] } navigator.serviceWorker.controller.postMessage(newPayload) } _resetCache (cb) { const reset = () => { this._send({ action: 'RESET' }, cb) } if (navigator.serviceWorker.controller) { reset() } else { navigator.serviceWorker.oncontrollerchange = reset } } ensureInitialized () { if (this.serviceWorkerState) { return } this.serviceWorkerState = 'REGISTERING' navigator.serviceWorker.register('/_next-prefetcher.js') // Reset the cache after registered // We don't need to have any old caches since service workers lives beyond // life time of the webpage. // With this prefetching won't work 100% if multiple pages of the same app // loads in the same browser in same time. // Basically, cache will only have prefetched resourses for the last loaded // page of a given app. // We could mitigate this, when we add a hash to a every file we fetch. this._resetCache((err) => { if (err) throw err this.serviceWorkerState = 'REGISTERED' this.serviceWorkerReadyCallbacks.forEach(cb => cb()) this.serviceWorkerReadyCallbacks = [] }) } } function hasServiceWorkerSupport () { return (typeof navigator !== 'undefined' && navigator.serviceWorker) } const PREFETCHED_URLS = {} let messenger if (hasServiceWorkerSupport()) { messenger = new Messenger() } export function prefetch (href) { if (!hasServiceWorkerSupport()) return if (!isLocal(href)) return // Register the service worker if it's not. messenger.ensureInitialized() let { pathname } = urlParse(href) // Add support for the index page if (pathname === '/') { pathname = '/index' } const url = `${pathname}.json` if (PREFETCHED_URLS[url]) return messenger.send({ action: 'ADD_URL', url: url }) PREFETCHED_URLS[url] = true } export default class LinkPrefetch extends React.Component { render () { const { href } = this.props if (this.props.prefetch !== false) { prefetch(href) } return () } }