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next.js/packages/next/client/page-loader.js

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/* global document */
import mitt from 'next-server/dist/lib/mitt'
// smaller version of https://gist.github.com/igrigorik/a02f2359f3bc50ca7a9c
function supportsPreload (list) {
if (!list || !list.supports) {
return false
}
try {
return list.supports('preload')
} catch (e) {
return false
}
}
const hasPreload = supportsPreload(document.createElement('link').relList)
export default class PageLoader {
constructor (buildId, assetPrefix) {
this.buildId = buildId
this.assetPrefix = assetPrefix
this.pageCache = {}
this.prefetchCache = new Set()
this.pageRegisterEvents = mitt()
this.loadingRoutes = {}
}
normalizeRoute (route) {
if (route[0] !== '/') {
throw new Error(`Route name should start with a "/", got "${route}"`)
}
route = route.replace(/\/index$/, '/')
if (route === '/') return route
return route.replace(/\/$/, '')
}
loadPage (route) {
route = this.normalizeRoute(route)
return new Promise((resolve, reject) => {
const fire = ({ error, page }) => {
this.pageRegisterEvents.off(route, fire)
delete this.loadingRoutes[route]
if (error) {
reject(error)
} else {
resolve(page)
}
}
// If there's a cached version of the page, let's use it.
const cachedPage = this.pageCache[route]
if (cachedPage) {
const { error, page } = cachedPage
error ? reject(error) : resolve(page)
return
}
// Register a listener to get the page
this.pageRegisterEvents.on(route, fire)
// If the page is loading via SSR, we need to wait for it
// rather downloading it again.
if (document.getElementById(`__NEXT_PAGE__${route}`)) {
return
}
// Load the script if not asked to load yet.
if (!this.loadingRoutes[route]) {
this.loadScript(route)
this.loadingRoutes[route] = true
}
})
}
loadScript (route) {
route = this.normalizeRoute(route)
const scriptRoute = route === '/' ? '/index.js' : `${route}.js`
const script = document.createElement('script')
const url = `${this.assetPrefix}/_next/static/${encodeURIComponent(this.buildId)}/pages${scriptRoute}`
script.crossOrigin = process.crossOrigin
script.src = url
script.onerror = () => {
const error = new Error(`Error when loading route: ${route}`)
error.code = 'PAGE_LOAD_ERROR'
this.pageRegisterEvents.emit(route, { error })
}
document.body.appendChild(script)
}
// This method if called by the route code.
registerPage (route, regFn) {
const register = () => {
try {
const { error, page } = regFn()
this.pageCache[route] = { error, page }
this.pageRegisterEvents.emit(route, { error, page })
} catch (error) {
this.pageCache[route] = { error }
this.pageRegisterEvents.emit(route, { error })
}
}
if (process.env.NODE_ENV !== 'production') {
// Wait for webpack to become idle if it's not.
// More info: https://github.com/zeit/next.js/pull/1511
if (module.hot && module.hot.status() !== 'idle') {
console.log(`Waiting for webpack to become "idle" to initialize the page: "${route}"`)
const check = (status) => {
if (status === 'idle') {
module.hot.removeStatusHandler(check)
register()
}
}
module.hot.status(check)
return
}
}
register()
}
async prefetch (route) {
route = this.normalizeRoute(route)
const scriptRoute = route === '/' ? '/index.js' : `${route}.js`
if (this.prefetchCache.has(scriptRoute)) {
return
}
this.prefetchCache.add(scriptRoute)
// Inspired by quicklink, license: https://github.com/GoogleChromeLabs/quicklink/blob/master/LICENSE
// Don't prefetch if the user is on 2G / Don't prefetch if Save-Data is enabled
if ('connection' in navigator) {
if ((navigator.connection.effectiveType || '').indexOf('2g') !== -1 || navigator.connection.saveData) {
return
}
}
// Feature detection is used to see if preload is supported
// If not fall back to loading script tags before the page is loaded
// https://caniuse.com/#feat=link-rel-preload
if (hasPreload) {
const link = document.createElement('link')
link.rel = 'preload'
link.crossOrigin = process.crossOrigin
link.href = `${this.assetPrefix}/_next/static/${encodeURIComponent(this.buildId)}/pages${scriptRoute}`
link.as = 'script'
document.head.appendChild(link)
return
}
if (document.readyState === 'complete') {
await this.loadPage(route)
} else {
return new Promise((resolve, reject) => {
window.addEventListener('load', () => {
this.loadPage(route).then(() => resolve(), reject)
})
})
}
}
clearCache (route) {
route = this.normalizeRoute(route)
delete this.pageCache[route]
delete this.loadingRoutes[route]
const script = document.getElementById(`__NEXT_PAGE__${route}`)
if (script) {
script.parentNode.removeChild(script)
}
}
}