public/js/app: Add instant page

1 files changed, 206 insertions, 0 deletions

diff --git a/public/js/app.js b/public/js/app.js
index 5804fab..ddfdc3e 100644
--- a/public/js/app.js
+++ b/public/js/app.js
@@ -608,3 +608,209 @@ window.onscroll = function() {
 imageZoom = mediumZoom('[data-image-zoom]');
 imageZoom.on('open', function(event) { addClass(navbar, 'navbar__headroom'); });
 imageZoom.on('close', function(event) { remClass(navbar, 'navbar__headroom'); });
+
+
+/**
+ * instant.page v3.0.0 - (C) 2019 Alexandre Dieulot - https://instant.page/license
+ */
+
+let mouseoverTimer
+let lastTouchTimestamp
+const prefetches = new Set()
+const prefetchElement = document.createElement('link')
+const isSupported = prefetchElement.relList && prefetchElement.relList.supports && prefetchElement.relList.supports('prefetch')
+                    && window.IntersectionObserver && 'isIntersecting' in IntersectionObserverEntry.prototype
+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
+let useViewport = false
+if ('instantIntensity' in document.body.dataset) {
+  const intensity = document.body.dataset.instantIntensity
+
+  if (intensity.substr(0, 'mousedown'.length) == 'mousedown') {
+    useMousedown = true
+    if (intensity == 'mousedown-only') {
+      useMousedownOnly = true
+    }
+  }
+  else if (intensity.substr(0, 'viewport'.length) == 'viewport') {
+    if (!(navigator.connection && (navigator.connection.saveData || navigator.connection.effectiveType.includes('2g')))) {
+      if (intensity == "viewport") {
+        /* Biggest iPhone resolution (which we want): 414 × 896 = 370944
+         * Small 7" tablet resolution (which we don’t want): 600 × 1024 = 614400
+         * Note that the viewport (which we check here) is smaller than the resolution due to the UI’s chrome */
+        if (document.documentElement.clientWidth * document.documentElement.clientHeight < 450000) {
+          useViewport = true
+        }
+      }
+      else if (intensity == "viewport-all") {
+        useViewport = true
+      }
+    }
+  }
+  else {
+    const milliseconds = parseInt(intensity)
+    if (!isNaN(milliseconds)) {
+      delayOnHover = milliseconds
+    }
+  }
+}
+
+if (isSupported) {
+  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)
+  }
+
+  if (useViewport) {
+    let triggeringFunction
+    if (window.requestIdleCallback) {
+      triggeringFunction = (callback) => {
+        requestIdleCallback(callback, {
+          timeout: 1500,
+        })
+      }
+    }
+    else {
+      triggeringFunction = (callback) => {
+        callback()
+      }
+    }
+
+    triggeringFunction(() => {
+      const intersectionObserver = new IntersectionObserver((entries) => {
+        entries.forEach((entry) => {
+          if (entry.isIntersecting) {
+            const linkElement = entry.target
+            intersectionObserver.unobserve(linkElement)
+            preload(linkElement.href)
+          }
+        })
+      })
+
+      document.querySelectorAll('a').forEach((linkElement) => {
+        if (isPreloadable(linkElement)) {
+          intersectionObserver.observe(linkElement)
+        }
+      })
+    })
+  }
+}
+
+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
+  }
+
+  preload(linkElement.href)
+}
+
+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})
+
+  mouseoverTimer = setTimeout(() => {
+    preload(linkElement.href)
+    mouseoverTimer = undefined
+  }, delayOnHover)
+}
+
+function mousedownListener(event) {
+  const linkElement = event.target.closest('a')
+
+  if (!isPreloadable(linkElement)) {
+    return
+  }
+
+  preload(linkElement.href)
+}
+
+function mouseoutListener(event) {
+  if (event.relatedTarget && event.target.closest('a') == event.relatedTarget.closest('a')) {
+    return
+  }
+
+  if (mouseoverTimer) {
+    clearTimeout(mouseoverTimer)
+    mouseoverTimer = undefined
+  }
+}
+
+function isPreloadable(linkElement) {
+  if (!linkElement || !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) {
+  if (prefetches.has(url)) {
+    return
+  }
+
+  const prefetcher = document.createElement('link')
+  prefetcher.rel = 'prefetch'
+  prefetcher.href = url
+  document.head.appendChild(prefetcher)
+
+  prefetches.add(url)
+}