Create displayName util (#2286)

lib/dynamic.js

 import React from 'react'
+import { getDisplayName } from './utils'
 
 let currentChunks = new Set()
 
@@ -55,7 +56,7 @@ export default function dynamicComponent (p, o) {
     loadComponent () {
       promise.then((AsyncComponent) => {
         // Set a readable displayName for the wrapper component
-        const asyncCompName = AsyncComponent.displayName || AsyncComponent.name
+        const asyncCompName = getDisplayName(AsyncComponent)
         if (asyncCompName) {
           DynamicComponent.displayName = `DynamicComponent for ${asyncCompName}`
         }

lib/side-effect.js

 import React, { Component } from 'react'
+import { getDisplayName } from './utils'
 
 export default function withSideEffect (reduceComponentsToState, handleStateChangeOnClient, mapStateOnServer) {
   if (typeof reduceComponentsToState !== 'function') {
@@ -13,10 +14,6 @@ export default function withSideEffect (reduceComponentsToState, handleStateChan
     throw new Error('Expected mapStateOnServer to either be undefined or a function.')
   }
 
-  function getDisplayName (WrappedComponent) {
-    return WrappedComponent.displayName || WrappedComponent.name || 'Component'
-  }
-
   return function wrap (WrappedComponent) {
     if (typeof WrappedComponent !== 'function') {
       throw new Error('Expected WrappedComponent to be a React component.')

lib/utils.js

@@ -42,12 +42,16 @@ export function printAndExit (message, code = 1) {
   process.exit(code)
 }
 
+export function getDisplayName (Component) {
+  return Component.displayName || Component.name || 'Unknown'
+}
+
 export async function loadGetInitialProps (Component, ctx) {
   if (!Component.getInitialProps) return {}
 
   const props = await Component.getInitialProps(ctx)
   if (!props && (!ctx.res || !ctx.res.finished)) {
-    const compName = Component.displayName || Component.name
+    const compName = getDisplayName(Component)
     const message = `"${compName}.getInitialProps()" should resolve to an object. But found "${props}" instead.`
     throw new Error(message)
   }