How to pass props to {this.props.children}

Question

I'm trying to find the proper way to define some components which could be used in a generic way:

<Parent>
  <Child value="1">
  <Child value="2">
</Parent>

There is a logic going on for rendering between parent and children components of course, you can imagine <select> and <option> as an example of this logic.

This is a dummy implementation for the purpose of the question:

var Parent = React.createClass({
  doSomething: function(value) {
  },
  render: function() {
    return (<div>{this.props.children}</div>);
  }
});

var Child = React.createClass({
  onClick: function() {
    this.props.doSomething(this.props.value); // doSomething is undefined
  },
  render: function() {
    return (<div onClick={this.onClick}></div>);
  }
});

The question is whenever you use {this.props.children} to define a wrapper component, how do you pass down some property to all its children?

Answer 1

Cloning children with new props

You can use React.Children to iterate over the children, and then clone each element with new props (shallow merged) using React.cloneElement. For example:

const Child = ({ doSomething, value }) => (
    <button onClick={() => doSomething(value)}>Click Me</button>
);

class Parent extends React.Component{
    doSomething = value => {
        console.log("doSomething called by child with value:", value);
    }

    render() {
        const childrenWithProps = React.Children.map(this.props.children, child => {
            // checking isValidElement is the safe way and avoids a typescript error too
            if (React.isValidElement(child)) {
                return React.cloneElement(child, { doSomething: this.doSomething });
            }
            return child;
        });

        return <div>{childrenWithProps}</div>;
    }
}

function App() {
    return (
        <Parent>
            <Child value={1} />
            <Child value={2} />
        </Parent>
    );
}

ReactDOM.render(<App />, document.getElementById("container"));

<script src="https://unpkg.com/react@17/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.production.min.js"></script>
<div id="container"></div>

Calling children as a function

Alternatively, you can pass props to children with render props. In this approach, the children (which can be children or any other prop name) is a function which can accept any arguments you want to pass and returns the children:

const Child = ({ doSomething, value }) => (
    <button onClick={() => doSomething(value)}>Click Me</button>
);

class Parent extends React.Component{
    doSomething = value => {
        console.log("doSomething called by child with value:", value);
    }

    render(){
        // note that children is called as a function and we can pass args to it
        return <div>{this.props.children(this.doSomething)}</div>
    }
};

function App(){
    return (
        <Parent>
            {doSomething => (
                <React.Fragment>
                    <Child doSomething={doSomething} value={1} />
                    <Child doSomething={doSomething} value={2} />
                </React.Fragment>
            )}
        </Parent>
    );
}

ReactDOM.render(<App />, document.getElementById("container"));

<script src="https://unpkg.com/react@17/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.production.min.js"></script>
<div id="container"></div>

Instead of <React.Fragment> or simply <> you can also return an array if you prefer.