refactor: move loadConfig into util

lib/prepare.js

 const path = require('path')
 const fs = require('fs-extra')
 const globby = require('globby')
-const yamlParser = require('js-yaml')
-const tomlParser = require('toml')
 const createMarkdown = require('./markdown')
+const loadConfig = require('./util/loadConfig')
 const tempPath = path.resolve(__dirname, 'app/.temp')
 const {
   inferTitle,
@@ -76,21 +75,7 @@ if (!Object.assign) Object.assign = require('object-assign')`
 
 async function resolveOptions (sourceDir) {
   const vuepressDir = path.resolve(sourceDir, '.vuepress')
-  const configPath = path.resolve(vuepressDir, 'config.js')
-  const configYmlPath = path.resolve(vuepressDir, 'config.yml')
-  const configTomlPath = path.resolve(vuepressDir, 'config.toml')
-
-  delete require.cache[configPath]
-
-  // resolve siteConfig
-  let siteConfig = {}
-  if (fs.existsSync(configYmlPath)) {
-    siteConfig = await parseConfig(configYmlPath)
-  } else if (fs.existsSync(configTomlPath)) {
-    siteConfig = await parseConfig(configTomlPath)
-  } else if (fs.existsSync(configPath)) {
-    siteConfig = require(configPath)
-  }
+  const siteConfig = loadConfig(vuepressDir)
 
   // normalize head tag urls for base
   const base = siteConfig.base || '/'
@@ -361,31 +346,3 @@ function sort (arr) {
     return 0
   })
 }
-
-async function parseConfig (file) {
-  const content = await fs.readFile(file, 'utf-8')
-  const [extension] = /.\w+$/.exec(file)
-  let data
-
-  switch (extension) {
-  case '.yml':
-  case '.yaml':
-    data = yamlParser.safeLoad(content)
-    break
-
-  case '.toml':
-    data = tomlParser.parse(content)
-    // reformat to match config since TOML does not allow different data type
-    // https://github.com/toml-lang/toml#array
-    const format = []
-    Object.keys(data.head).forEach(meta => {
-      data.head[meta].forEach(values => {
-        format.push([meta, values])
-      })
-    })
-    data.head = format
-    break
-  }
-
-  return data || {}
-}

lib/util/loadConfig.js

+const fs = require('fs-extra')
+const path = require('path')
+const yamlParser = require('js-yaml')
+const tomlParser = require('toml')
+
+module.exports = function loadConfig (vuepressDir, bustCache = false) {
+  const configPath = path.resolve(vuepressDir, 'config.js')
+  const configYmlPath = path.resolve(vuepressDir, 'config.yml')
+  const configTomlPath = path.resolve(vuepressDir, 'config.toml')
+
+  if (bustCache) {
+    delete require.cache[configPath]
+  }
+
+  // resolve siteConfig
+  let siteConfig = {}
+  if (fs.existsSync(configYmlPath)) {
+    siteConfig = parseConfig(configYmlPath)
+  } else if (fs.existsSync(configTomlPath)) {
+    siteConfig = parseConfig(configTomlPath)
+  } else if (fs.existsSync(configPath)) {
+    siteConfig = require(configPath)
+  }
+
+  return siteConfig
+}
+
+function parseConfig (file) {
+  const content = fs.readFileSync(file, 'utf-8')
+  const [extension] = /.\w+$/.exec(file)
+  let data
+
+  switch (extension) {
+  case '.yml':
+  case '.yaml':
+    data = yamlParser.safeLoad(content)
+    break
+
+  case '.toml':
+    data = tomlParser.parse(content)
+    // reformat to match config since TOML does not allow different data type
+    // https://github.com/toml-lang/toml#array
+    const format = []
+    Object.keys(data.head).forEach(meta => {
+      data.head[meta].forEach(values => {
+        format.push([meta, values])
+      })
+    })
+    data.head = format
+    break
+  }
+
+  return data || {}
+}