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next.js/lib/prefetch.js

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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 (<Link {...this.props} />)
}
}