refactor(core): adjust directory structure:

src/core/fetch/ajax.js

@@ -0,0 +1,37 @@
+import progressbar from '../render/progressbar'
+import { noop } from '../util/core'
+
+/**
+ * Simple ajax get
+ * @param  {String} url
+ * @param {Boolean} [loading=false] has loading bar
+ * @return { then(resolve, reject), abort }
+ */
+export function get (url, hasLoading = false) {
+  const xhr = new XMLHttpRequest()
+
+  xhr.open('GET', url)
+  xhr.send()
+
+  return {
+    then: function (success, error = noop) {
+      const on = xhr.addEventListener
+
+      if (hasLoading) {
+        const id = setInterval(_ => progressbar({}), 500)
+
+        on('progress', progressbar)
+        on('loadend', evt => {
+          progressbar(evt)
+          clearInterval(id)
+        })
+      }
+
+      on('error', error)
+      on('load', ({ target }) => {
+        target.status >= 400 ? error(target) : success(target.response)
+      })
+    },
+    abort: () => xhr.readyState !== 4 && xhr.abort()
+  }
+}

src/core/fetch/index.js

@@ -0,0 +1,13 @@
+import { callHook } from '../init/lifecycle'
+
+export function fetchMixin (Docsify) {
+  Docsify.prototype.$fetch = function () {
+  }
+}
+
+export function initFetch (vm) {
+  vm.$fetch(result => {
+    vm.$resetEvents()
+    callHook(vm, 'doneEach')
+  })
+}