reactjs - When should I be using React.cloneElement vs this.props.children?

Question

I am still a noob at React and in many examples on the internet, I see this variation in rendering child elements which I find confusing. Normally I see this:

class Users extends React.Component {
  render() {
    return (
      <div>
        <h2>Users</h2>
        {this.props.children}
      </div>
    )
  }
}

But then I see an example like this:

<ReactCSSTransitionGroup
     component="div"
     transitionName="example"
     transitionEnterTimeout={500}
     transitionLeaveTimeout={500}
     >
     {React.cloneElement(this.props.children, {
       key: this.props.location.pathname
      })}
</ReactCSSTransitionGroup>

Now I understand the api but the docs don't exactly make clear when I should be using it.

So what does one do which the other can't? Could someone explain this to me with better examples?

Answer 1

props.children isn't the actual children; It is the descriptor of the children. So you don't have actually anything to change; you can't change any props, or edit any functionality; you can only read from it. If you need to make any modifications you have to create new elements using React.CloneElement.

https://egghead.io/lessons/react-use-react-cloneelement-to-extend-functionality-of-children-components

An example:

main render function of a component such as App.js:

render() {   
    return(
            <Paragraph>
              <Sentence>First</Sentence>
              <Sentence>Second</Sentence>
              <Sentence>Third</Sentence>
            </Paragraph>   
    ) 
}

now let's say you need to add an onClick to each child of Paragraph; so in your Paragraph.js you can do:

render() {
        return (
          <div>
          {React.Children.map(this.props.children, child => {
            return React.cloneElement(child, {
              onClick: this.props.onClick })   
         })}
         </div>
       ) 
}

then simply you can do this:

render() {   
  return(
        <Paragraph onClick={this.onClick}>
          <Sentence>First</Sentence>
          <Sentence>Second</Sentence>
          <Sentence>Third</Sentence>
        </Paragraph>   
   ) 
}

Note: the React.Children.map function will only see the top level elements, it does not see any of the things that those elements render; meaning that you are providing the direct props to children (here the <Sentence /> elements). If you need the props to be passed down further, let's say you will have a <div></div> inside one of the <Sentence /> elements that wants to use the onClick prop then in that case you can use the Context API to do it. Make the Paragraph the provider and the Sentence elements as consumer.