Reconciliation has bug that is occured when client starts hydration

2018-04-28 17:02:34

Do you want to request a feature or report a bug?

What is the current behavior?

// Static.js
import React from 'react'

function Static() {
  return (
    <div className="i am static" style={{ backgroundColor: 'red', width: '100%', height: '300px' }}>

export default Static
// Dynamic.js
import React from 'react'

function Dynamic() {
  return (
    <div className="i am dynamic" style={{ backgroundColor: 'blue', width: '100%', height: '300px' }}>

export default Dynamic
// App.js
import React from 'react'
import Static from './Static'
import Dynamic from './Dynamic'

class App extends React.Component {
  constructor(props) {
    this.mounted = false
    this.state = {
      loaded: !isBrowser

    if (isBrowser) {
      new Promise((resolve) => {
        setTimeout(() => {
          const nextState = {
            loaded: true
          if (this.mounted) {
          } else {
            this.state = nextState
        }, 200)

  componentDidMount() {
    this.mounted = true

  render() {
    return (
        {this.state.loaded ? <Dynamic /> : null}
        <Static />

export default App

First, Server sends React App without any asynchronous component loading.

Second, Client starts hydration with loading <Dynamic /> component asynchronously.
(In our real production, We used code splitting with webpack and loaded it with import(). In this example, I just controlled loaded state for making app simple.)
During <Dynamic /> is being loaded, App renders null instead.

Finally, Let's see the result.

screen shot 2018-04-29 at 1 43 47 am

Why background-color of <Static /> component is changed to blue?

screen shot 2018-04-29 at 1 47 50 am

<Dynamic /> took <Static /> for dinner.

AFAIK, React don't touch the result of client rendering if it is different with server html.
When I moved to another page through client-side routes I cannot find this situation.

So, I guess it occurs only when client hydrates the result of server-side rendering .

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle ( or CodeSandbox ( example below:

You can check it easily with
Clone it, run yarn, yarn start, and open http://localhost:3000.

What is the expected behavior?
screen shot 2018-04-29 at 1 44 08 am

screen shot 2018-04-29 at 1 57 42 am

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

React 16.3.2
Browser: Chrome (Safari too.)
OS: MacOS (Windows or Linux too.)

React 15 works well without any bug.
Check it at
(react-15 branch)

2018-04-28 17:09:51

Does this help?


2018-04-28 17:21:13

Okay it helps me partly, but I have one question.

Do you want to say this problem is intended, and it is to be expected?
Otherwise do you just hold it on for performance, user experience, or any other issues?

In my case, It's just not to make client different with server.
I want to make same between client and server but there is a space at client for performance issue.
server (#1) -> client (#2, in a short time for loading chunk asynchronously) -> client (#1)

In generic case, server and client are same.
server (#1) -> client (#1)

In #10591 case, server and client are different. That's all.
server (#1) -> client (#2)

Is there any methods to implement it?

2018-07-04 00:33:59

@gaearon Can you assign this to me? or should I just investigate and submit PR?

2018-08-02 19:23:19

I want to make same between client and server but there is a space at client for performance issue.

We don't have a good solution for temporary mismatches, sorry. We probably will in the future.

2018-08-16 07:33:23

It's okay. I solved it with rendering root element of child component(ex, div, p, ...) instead of null during component is loading it asynchronously.

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