feat: add Hot Reload support

Thanks to @likun7981 for the original idea!

README.md

@@ -340,6 +340,17 @@ import { getState } from 'loadable-components'
 window.snapSaveState = () => getState()
 ```
 
+### Hot Reloading
+
+Loadable Components is Hot Reload friendly, it works out of the box with [React Hot Loader](https://github.com/gaearon/react-hot-loader) without adding a single line of code. All components are loaded when a reload occurs, if you want to disable this behaviour, you can set a global config:
+
+```js
+import { setConfig } from 'loadable-components'
+
+// Disable automatic "load" of components
+setConfig({ hotReload: false })
+```
+
 ## API Reference
 
 ### loadable

src/config.js

@@ -0,0 +1,9 @@
+/* eslint-disable no-underscore-dangle */
+
+const _config = {
+  // Automatically load components in hot reload environment
+  hotReload: process.env.NODE_ENV === 'development',
+}
+
+export const setConfig = config => Object.assign(_config, config)
+export const getConfig = () => _config

src/config.test.js

@@ -0,0 +1,9 @@
+import { getConfig, setConfig } from './config'
+
+describe('config', () => {
+  it('should set and get config', () => {
+    expect(getConfig()).toEqual({ hotReload: false })
+    setConfig({ hotReload: true })
+    expect(getConfig()).toEqual({ hotReload: true })
+  })
+})

src/index.js

@@ -4,4 +4,5 @@ export { default as loadComponents } from './loadComponents'
 export { default as getState } from './getState'
 export { LOADABLE } from './constants'
 export { default } from './loadable'
+export { setConfig } from './config'
 export const componentTracker = tracker

src/loadable.js

@@ -3,6 +3,7 @@ import React from 'react'
 import { LOADABLE } from './constants'
 import resolveModuleDefault from './utils/resolveModuleDefault'
 import * as componentTracker from './componentTracker'
+import { getConfig } from './config'
 
 const EmptyComponent = () => null
 
@@ -93,6 +94,10 @@ function loadable(
 
   LoadableComponent[LOADABLE] = () => LoadableComponent
 
+  if (module && module.hot && getConfig().hotReload) {
+    LoadableComponent.load()
+  }
+
   if (modules) {
     const id = componentTracker.track(LoadableComponent, modules)
     LoadableComponent.componentId = id