Functions are not valid as a React child. This may happen if you return a Component instead of from render

Question

I have written a Higher Order Component:

import React from 'react';


const NewHOC = (PassedComponent) => {
    return class extends React.Component {
        render(){
            return (
                <div>
                    <PassedComponent {...this.props}/>
                </div>
            )
        }
    }
}

export default NewHOC;

I am using the above in my App.js:

import React from 'react';
import Movie from './movie/Movie';
import MyHOC from './hoc/MyHOC';
import NewHOC from './hoc/NewHOC';
export default class App extends React.Component {
  render() {
   return (
    <div>
     Hello From React!!
     <NewHOC>
        <Movie name="Blade Runner"></Movie>
     </NewHOC>
    </div>
   );
  }
 }

But, the warning I am getting is:

Warning: Functions are not valid as a React child. This may happen if you return a Component instead of <Component /> from render. Or maybe you meant to call this function rather than return it. in NewHOC (created by App) in div (created by App) in App

The Movie.js file is:

import React from "react";

export default class Movie extends React.Component{
    render() {
        return <div>
            Hello from Movie {this.props.name}
            {this.props.children}</div>
    }
}

What am I doing wrong?

Answer 1

You are using it as a regular component, but it's actually a function that returns a component.

Try doing something like this:

const NewComponent = NewHOC(Movie)

And you will use it like this:

<NewComponent someProp="someValue" />

Here is a running example:

const NewHOC = (PassedComponent) => {
  return class extends React.Component {
    render() {
      return (
        <div>
          <PassedComponent {...this.props} />
        </div>
      )
    }
  }
}

const Movie = ({name}) => <div>{name}</div>

const NewComponent = NewHOC(Movie);

function App() {
  return (
    <div>
      <NewComponent name="Kill Bill" />
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"/>

So basically NewHOC is just a function that accepts a component and returns a new component that renders the component passed in. We usually use this pattern to enhance components and share logic or data.

You can read about HOCS in the docs and I also recommend reading about the difference between react elements and components

I wrote an article about the different ways and patterns of sharing logic in react.