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

Class Names

Firstly, if you're certain that you're extending from the correctly named class, e.g. React.Component, not React.component or React.createComponent, you may need to upgrade your React version. See answers below for more information on the classes to extend from.

Upgrade React

React has only supported ES6-style classes since version 0.13.0 (see their official blog post on the support introduction here.

Before that, when using:

class HelloMessage extends React.Component

you were attempting to use ES6 keywords (extends) to subclass from a class which wasn't defined using ES6 class. This was likely why you were running into strange behaviour with super definitions etc.

So, yes, TL;DR - update to React v0.13.x.

Circular Dependencies

This can also occur if you have circular import structure. One module importing another and the other way around. In this case you just need to refactor your code to avoid it. More info

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

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.