refactor: improve hmr code generation

lib/hotReload.js

 const hotReloadAPIPath = require.resolve('vue-hot-reload-api')
 
-module.exports = function genHotReloadCode (id, functional) {
+exports.genHotReloadCode = (id, functional) => {
   // TODO handle CSSModules and style injection disposal
+  return wrap(`
+    if (!module.hot.data) {
+      api.createRecord('${id}', component.options)
+    } else {
+      api.${functional ? `rerender` : `reload`}('${id}', component.options)
+    }
+  `)
+}
+
+exports.genTemplateHotReloadCode = id => {
+  return wrap(`
+    if (module.hot.data) {
+      require('${hotReloadAPIPath}').rerender('${id}', {
+        render: render,
+        staticRenderFns: staticRenderFns
+      })
+    }
+  `)
+}
+
+function wrap (inner) {
   return `
 /* hot reload */
 if (module.hot) {
@@ -9,11 +30,7 @@ if (module.hot) {
   api.install(require('vue'))
   if (api.compatible) {
     module.hot.accept()
-    if (!module.hot.data) {
-      api.createRecord('${id}', component.options)
-    } else {
-      api.${functional ? `rerender` : `reload`}('${id}', component.options)
-    }
+    ${inner.trim()}
   }
 }
   `.trim()

lib/index.js

@@ -5,7 +5,7 @@ const qs = require('querystring')
 const loaderUtils = require('loader-utils')
 const selectBlock = require('./selector')
 const plugin = require('./plugin')
-const genHotReloadCode = require('./hotReload')
+const { genHotReloadCode } = require('./hotReload')
 const componentNormalizerPath = require.resolve('./runtime/componentNormalizer')
 
 module.exports = function (source) {

lib/template-loader/index.js

@@ -6,7 +6,7 @@ const compiler = require('vue-template-compiler')
 const transpile = require('vue-template-es2015-compiler')
 const transformAssetUrl = require('./modules/assetUrl')
 const transformSrcset = require('./modules/srcset')
-const hotReloadAPIPath = require.resolve('vue-hot-reload-api')
+const { genTemplateHotReloadCode } = require('../hotReload')
 
 // Loader that compiles raw template into JavaScript functions.
 // This is injected by the global pitcher (../pitch) for template
@@ -141,16 +141,10 @@ function actuallyCompile (sourceTemplate, options, loaderContext, query) {
     }
     code += `export { render, staticRenderFns }`
   }
+
   // hot-reload
   if (needsHotReload) {
-    code +=
-      '\nif (module.hot) {\n' +
-      '  module.hot.accept()\n' +
-      '  if (module.hot.data) {\n' +
-      '    require("' + hotReloadAPIPath + '")' +
-      '      .rerender("' + options.id + '", { render: render, staticRenderFns: staticRenderFns })\n' +
-      '  }\n' +
-      '}'
+    code += genTemplateHotReloadCode(id)
   }
 
   return code