[reactjs] reactjs giving error Uncaught TypeError: Super expression must either be null or a function, not undefined

I am using reactjs.

When I run the code below the browser says:

Uncaught TypeError: Super expression must either be null or a function, not undefined

Any hints at all as to what is wrong would be appreciated.

First the line used to compile the code:

browserify -t reactify -t babelify examples/temp.jsx  -o examples/public/app.js

And the code:

var React = require('react');

class HelloMessage extends React.Component {
  render() {
    return <div>Hello </div>;
  }
}

UPDATE: After burning in hellfire for three days on this problem I found that I was not using the latest version of react.

Install globally:

sudo npm install -g [email protected]

install locally:

npm install [email protected]

make sure the browser is using the right version too:

<script type="text/javascript" src="react-0.13.2.js"></script>

Hope this saves someone else three days of precious life.

I experienced this when missing an export statement for the JSX class.

For example:

class MyComponent extends React.Component {
}
export default MyComponent // <- add me

There might be a third party package causing this. In our case it was react-dazzle. We have similar settings to that of @steine (see this answer above).

In order to find the problematic package I ran the webpack build locally with production mode and thus was able to find the problematic package in the stack trace. So for us this provided the solution and I was able to keep the uglification.

For me I forgot default. So I wrote export class MyComponent instead of export default class MyComponent

If you are running a dev watch mode stop out and rebuild. I converted an ES6 module to a React Component and it only worked after a rebuild (vs a watch build).

Webpack 4 Chunks and Hashes with Uglification by TerserPlugin

This can occur when Webpack uses chunks and hashes with minification and unglification via TerserPlugin (currently on version 1.2.3). In my case the error was narrowed down to the uglification by the Terser Plugin of my vendors.[contenthash].js bundle which holds my node_modules. Everything worked when not using hashes.

Solution was to exclude the bundle in the uglification options:

optimization: {
  minimizer: [
    new TerserPlugin({
      chunkFilter: (chunk) => {
        // Exclude uglification for the `vendors` chunk
        if (chunk.name === 'vendors') {
          return false;
        }
        return true;
      },
    }),
  ],
}

More info

In my case, I was using a npm module with peer dependencies. The error was caused by the wrong 'external' config in he module's webpack config:

  externals: {
    react: 'react',
    react: 'prop-types',
  },

It should be:

externals: {
    react: 'react',
    ['prop-types']: 'prop-types',
  },

My conditions

• Create-React-App
• React-scripts v3.2
• Froala rich text editor v3.1
• Development mode worked fine
• The production build was broken with the error mentioned in the question

Solution to my problem

Downgrade Froala to v3.0.

Something in v3.1 broke our Create React App build process.

Update: Use react scripts v3.3

We discovered that there was an issue between React Scripts 3.2 and Froala 3.1.

Updating to React Scripts v3.3 allowed us to upgrade to Froala 3.1.

I had this problem because my react and react-dom versions were not matching after a merge.

I fixed it by manually entering the version number I wanted and re-running npm install.

Here is one answer:

import React, { Component } from 'react'; // NOT 'react-dom'

Not correct for this answer but for others with same error my ridiculously silly mistake could potentially help.

Stupidly,my issue was using function notation by including () following the class name.

Make sure your syntax is correct. And you've imported & exported any external components/modules with the correct names and paths.

This template should work fine if you have a newish version of react installed:

import React, { Component } from 'react'

class ExampleClass extends Component {

    render(){
        return(
            <div>

            </div>
        )
    }
}

export default ExampleClass 

Using Babel (5.8) I get the same error if I try to use the expression export default in combination with some other export:

export const foo = "foo"
export const bar = "bar"
export default function baz() {}

It can also be caused by a typo error, so instead of Component with capital C, you have component with lower c, for example:

React.component //wrong.
React.Component //correct.

Note: The source of this error is may be because there is React and we think automatically what comes next should be a react method or property starting with a lowercase letter, but in fact it is another Class(Component) which should start with a capital case letter.

For any other persons, that may develop this issue. You could also check that the component method in React.Component is capitalized. I had that same issue and what caused it was that I wrote:

class Main extends React.component {
  //class definition
}

I changed it to

class Main extends React.Component {
  //class definition
}

and everything worked well

I am going to contribute another possible solution, one that worked for me. I was using the convenience index to collection all components into one file.

I don't believe at the time of writing this is officially supported by babel, and throws typescript into a spin - however I've seen it used in many projects and is definitely convenient.

However, when used in combination with inheritance it seems to throw the error presented in the question above.

A simple solution is, for modules that act as parents need to be imported directly instead of via a convenience index file.

./src/components/index.js

export Com1 from './com-1/Com1';
export Com2 from './com-2/Com2';
export Com3 from './com-3/Com3';
export Parent1 from './parent/Parent1';

./src/components/com-1/Com1.js

import { Com2, Com3 } from '../index';

// This works fine
class Com1 {        
    render() {
        return (
            <div>
                <Com2 {...things} />
                <Com3 {...things} />
            </div>
        );
    }
}

./src/components/com-3/Com3.js

import { Parent } from '../index';

// This does _not_ work
class Com3 extends Parent {        
}

./src/components/com-3/Com3.js

import Parent from '../parent/Parent';

// This does work
class Com3 extends Parent {        
}

In my case it was React.Element change to React.Component that make fix for this error.

Look if you have a typo error in your importation or your class generation, it could be simply that.

I have same issue, just change from Navigator to {Navigator}

import Navigator from 'react-native-deprecated-custom-components'
// to
import {Navigator} from 'react-native-deprecated-custom-components'

I experienced this error while importing component like:

import React, { Components } from 'react';

instead of

import React, { Component } from 'react';

I've seen this error occur due to 'comments' in the bundle generated by webpack. Using 'pathinfo'= true in webpack.config.js can cause this issue:

webpack.config.js

module.exports = {
  output: {
    pathinfo: true,
  }
}

'pathinfo' defaults to true in development and false in production mode. https://webpack.js.org/configuration/output/#outputpathinfo Try setting this value to false to resolve the issue.

This can also happen if you are not using a plugin to strip the comments from the build output. Try using UglifyJs (https://www.npmjs.com/package/uglifyjs-webpack-plugin/v/1.3.0):

webpack.config.js

const UglifyJsPlugin = require('uglifyjs-webpack-plugin')

module.exports = {
  ...
  optimization: {
    minimizer: [new UglifyJsPlugin(
      new UglifyJsPlugin({
        uglifyOptions: {
          output: {
            comments: false
          }
        }
      }),
    )],
  }
}

You can also receive this if you are attempting to execute React.Component with an erroneous () in your class definition.

export default class MyComponent extends React.Component() {}
                                                        ^^ REMOVE

Which I sometimes manage to do when I'm converting from a stateless functional component to a class.

For those using react-native:

import React, {
  Component,
  StyleSheet,
} from 'react-native';

may produce this error.

Whereas referencing react directly is the more stable way to go:

import React, { Component } from 'react';
import { StyleSheet } from 'react-native';

In my case, I fixed this error by change export default class yourComponent extends React.Component() {} to export default class yourComponent extends React.Component {}. Yes delete the parenthesis () fixed the error.

Check for the Classes you extend actually exists, few React methods are depreciated, It also might be a Typo error 'React.Components' instead of 'React.Component'

Good Luck!!

I've seen this error when you have a circular dependency.

class A extends B {}
class B extends C {}
class C extends A {}

Change import React from 'react-dom to import React, {Component} from 'react'
And change class Classname extends React.Component to class Classname extends Component
If you are using the latest version of React(16.8.6 as of now).

I got this when I tried to use react-i18next's Translation on the parent class and the child. It was being translated twice!

In my case I was using:

class Root extends React.Component() {
// THIS IS WORNG
// After React.Component () <- WRONG!!
}

which was wrong but correct is:

class Root extends React.Component {
// THIS IS CORRECT
// That -> '()' after React.Component was typo
}

also make sure there is
v React.Component
NOT
? React.component or React.Components

This means that you want subclass something, which should be Class, but is undefined. The reasons might be:

• typo in Class extends ..., so you extending undefined variable
• typo in import ... from, so you import undefined from module
• referenced module does not contain the value, you want import (e.g. obsolete module - case with React), so you importing non existing value (undefined)
• typo in referenced module export ... statement, so it exports undefined variable
• referenced module missing export statement at all, so it exports just undefined

In my case, it turned out React <15.3.0 doesn't include React.PureComponent. So code like:

class MyClass extends React.PureComponent {
    //...
}

wouldn't work.

Another occurrence with Expo/react-native with typescript : sometimes when you are recompiling the typescript files in the middle of a packaging, the react packager is lost.

The only way to make my app run again is to clear the cache; if you are using the expo cli, you can press press R (that is an UPPERCASE 'R'); this will rebuild the whole bundle. Sometimes switching to development mode also helps....

Happened to me too when I used this :

class App extends React.Component(){

}

Instead of the right one :

class App extends React.Component{

}

Notice:- () in the first one which is the main cause of this problem

I`ve written

React.component

instead of React.Component That was my issue)) and was looking for this more than half an hour.

I got this when I had a typo on my import:

import {Comonent} from 'react';

This can also happen if you had used require instead of import within your code.

This worked for me:

import React, {Component} from 'react';

In my case, with react-native, the error was that I had

import React, {
  AppRegistry,
  Component,
  Text,
  View,
  TouchableHighlight
} from 'react-native';

instead of

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  View,
  Image,
  AsyncStorage
} from 'react-native';

If you are receiving this error and are using Browserify and browserify-shim (like in a Grunt task), you might have experienced a dumb moment like I did where you unintentionally told browserify-shim to treat React as already part of the global namespace (for example, loaded from a CDN).

If you want Browserify to include React as part of the transform, and not a separate file, make sure the line "react": "global:React" does not appear in the "browserify-shim" section in your packages.json file.