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/*! instant.page v2.0.0 - (C) 2019 Alexandre Dieulot - https://instant.page/license */
let urlToPreload
let mouseoverTimer
let lastTouchTimestamp
const prefetcher = document.createElement('link')
const isSupported = prefetcher.relList && prefetcher.relList.supports && prefetcher.relList.supports('prefetch')
const isDataSaverEnabled = navigator.connection && navigator.connection.saveData
const allowQueryString = 'instantAllowQueryString' in document.body.dataset
const allowExternalLinks = 'instantAllowExternalLinks' in document.body.dataset
const useWhitelist = 'instantWhitelist' in document.body.dataset
let delayOnHover = 65
let useMousedown = false
let useMousedownOnly = false
if ('instantIntensity' in document.body.dataset) {
if (document.body.dataset.instantIntensity.substr(0, 'mousedown'.length) == 'mousedown') {
useMousedown = true
if (document.body.dataset.instantIntensity == 'mousedown-only') {
useMousedownOnly = true
}
} else {
const milliseconds = parseInt(document.body.dataset.instantIntensity)
if (!isNaN(milliseconds)) {
delayOnHover = milliseconds
}
}
}
if (isSupported && !isDataSaverEnabled) {
prefetcher.rel = 'prefetch'
document.head.appendChild(prefetcher)
const eventListenersOptions = {
capture: true,
passive: true,
}
if (!useMousedownOnly) {
document.addEventListener('touchstart', touchstartListener, eventListenersOptions)
}
if (!useMousedown) {
document.addEventListener('mouseover', mouseoverListener, eventListenersOptions)
} else {
document.addEventListener('mousedown', mousedownListener, eventListenersOptions)
}
}
function touchstartListener(event) {
/* Chrome on Android calls mouseover before touchcancel so `lastTouchTimestamp`
* must be assigned on touchstart to be measured on mouseover. */
lastTouchTimestamp = performance.now()
const linkElement = event.target.closest('a')
if (!isPreloadable(linkElement)) {
return
}
linkElement.addEventListener('touchcancel', touchendAndTouchcancelListener, {
passive: true
})
linkElement.addEventListener('touchend', touchendAndTouchcancelListener, {
passive: true
})
urlToPreload = linkElement.href
preload(linkElement.href)
}
function touchendAndTouchcancelListener() {
urlToPreload = undefined
stopPreloading()
}
function mouseoverListener(event) {
if (performance.now() - lastTouchTimestamp < 1100) {
return
}
const linkElement = event.target.closest('a')
if (!isPreloadable(linkElement)) {
return
}
linkElement.addEventListener('mouseout', mouseoutListener, {
passive: true
})
urlToPreload = linkElement.href
mouseoverTimer = setTimeout(() => {
preload(linkElement.href)
mouseoverTimer = undefined
}, delayOnHover)
}
function mousedownListener(event) {
const linkElement = event.target.closest('a')
if (!isPreloadable(linkElement)) {
return
}
linkElement.addEventListener('mouseout', mouseoutListener, {
passive: true
})
urlToPreload = linkElement.href
preload(linkElement.href)
}
function mouseoutListener(event) {
if (event.relatedTarget && event.target.closest('a') == event.relatedTarget.closest('a')) {
return
}
if (mouseoverTimer) {
clearTimeout(mouseoverTimer)
mouseoverTimer = undefined
}
urlToPreload = undefined
stopPreloading()
}
function isPreloadable(linkElement) {
if (!linkElement || !linkElement.href) {
return
}
if (urlToPreload == linkElement.href) {
return
}
if (useWhitelist && !('instant' in linkElement.dataset)) {
return
}
if (!allowExternalLinks && linkElement.origin != location.origin && !('instant' in linkElement.dataset)) {
return
}
if (!['http:', 'https:'].includes(linkElement.protocol)) {
return
}
if (linkElement.protocol == 'http:' && location.protocol == 'https:') {
return
}
if (!allowQueryString && linkElement.search && !('instant' in linkElement.dataset)) {
return
}
if (linkElement.hash && linkElement.pathname + linkElement.search == location.pathname + location.search) {
return
}
if ('noInstant' in linkElement.dataset) {
return
}
return true
}
function preload(url) {
prefetcher.href = url
}
function stopPreloading() {
prefetcher.removeAttribute('href')
}