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Turbolinks Prefetching
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const hoverTime = 400 | |
const fetchers = {} | |
const doc = document.implementation.createHTMLDocument('prefetch') | |
function fetchPage (url, success) { | |
const xhr = new XMLHttpRequest() | |
xhr.open('GET', url) | |
xhr.setRequestHeader('VND.PREFETCH', 'true') | |
xhr.setRequestHeader('Accept', 'text/html') | |
xhr.onreadystatechange = () => { | |
if (xhr.readyState !== XMLHttpRequest.DONE) return | |
if (xhr.status !== 200) return | |
success(xhr.responseText) | |
} | |
xhr.send() | |
} | |
function prefetchTurbolink (url) { | |
fetchPage(url, responseText => { | |
doc.open() | |
doc.write(responseText) | |
doc.close() | |
const snapshot = Turbolinks.Snapshot.fromHTMLElement(doc.documentElement) | |
Turbolinks.controller.cache.put(url, snapshot) | |
}) | |
} | |
function prefetch (url) { | |
if (prefetched(url)) return | |
prefetchTurbolink(url) | |
} | |
function prefetched (url) { | |
return location.href === url || Turbolinks.controller.cache.has(url) | |
} | |
function prefetching (url) { | |
return !!fetchers[url] | |
} | |
function cleanup (event) { | |
const element = event.target | |
clearTimeout(fetchers[element.href]) | |
element.removeEventListener('mouseleave', cleanup) | |
} | |
document.addEventListener('mouseover', event => { | |
if (!event.target.dataset.prefetch) return | |
const url = event.target.href | |
if (prefetched(url)) return | |
if (prefetching(url)) return | |
cleanup(event) | |
event.target.addEventListener('mouseleave', cleanup) | |
fetchers[url] = setTimeout(() => prefetch(url), hoverTime) | |
}) |
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