WIP - add extractor, generate snippet_data

node_modules/gatsby/cache-dir/prefetch.js

@@ -0,0 +1,76 @@
+const support = function(feature) {
+  if (typeof document === `undefined`) {
+    return false
+  }
+  const fakeLink = document.createElement(`link`)
+  try {
+    if (fakeLink.relList && typeof fakeLink.relList.supports === `function`) {
+      return fakeLink.relList.supports(feature)
+    }
+  } catch (err) {
+    return false
+  }
+  return false
+}
+
+const linkPrefetchStrategy = function(url) {
+  return new Promise((resolve, reject) => {
+    if (typeof document === `undefined`) {
+      reject()
+      return
+    }
+
+    const link = document.createElement(`link`)
+    link.setAttribute(`rel`, `prefetch`)
+    link.setAttribute(`href`, url)
+
+    link.onload = resolve
+    link.onerror = reject
+
+    const parentElement =
+      document.getElementsByTagName(`head`)[0] ||
+      document.getElementsByName(`script`)[0].parentNode
+    parentElement.appendChild(link)
+  })
+}
+
+const xhrPrefetchStrategy = function(url) {
+  return new Promise((resolve, reject) => {
+    const req = new XMLHttpRequest()
+    req.open(`GET`, url, true)
+
+    req.onload = () => {
+      if (req.status === 200) {
+        resolve()
+      } else {
+        reject()
+      }
+    }
+
+    req.send(null)
+  })
+}
+
+const supportedPrefetchStrategy = support(`prefetch`)
+  ? linkPrefetchStrategy
+  : xhrPrefetchStrategy
+
+const preFetched = {}
+
+const prefetch = function(url) {
+  return new Promise(resolve => {
+    if (preFetched[url]) {
+      resolve()
+      return
+    }
+
+    supportedPrefetchStrategy(url)
+      .then(() => {
+        resolve()
+        preFetched[url] = true
+      })
+      .catch(() => {}) // 404s are logged to the console anyway
+  })
+}
+
+export default prefetch