Pass Props to Parent Component in React.Js

Pass props to parent component in React.js

Edit: see the end examples for ES6 updated examples.

This answer simply handle the case of direct parent-child relationship. When parent and child have potentially a lot of intermediaries, check this answer.

Better implementation

Child: it really does not have to be more complicated than that.

var Child = React.createClass({
  render: function () {
    return <button onClick={this.props.onClick}>{this.props.text}</button>;
  },
});

Parent with single child: using the value it passes to the child

var Parent = React.createClass({
  getInitialState: function() {
     return {childText: "Click me! (parent prop)"};
  },
  render: function () {
    return (
      <Child onClick={this.handleChildClick} text={this.state.childText}/>
    );
  },
  handleChildClick: function(event) {
     // You can access the prop you pass to the children 
     // because you already have it! 
     // Here you have it in state but it could also be
     //  in props, coming from another parent.
     alert("The Child button text is: " + this.state.childText);
     // You can also access the target of the click here 
     // if you want to do some magic stuff
     alert("The Child HTML is: " + event.target.outerHTML);
  }
});

JsFiddle

Parent with list of children: you still have everything you need on the parent and don't need to make the child more complicated.

var Parent = React.createClass({
  getInitialState: function() {
     return {childrenData: [
         {childText: "Click me 1!", childNumber: 1},
         {childText: "Click me 2!", childNumber: 2}
     ]};
  },
  render: function () {
    var children = this.state.childrenData.map(function(childData,childIndex) {
        return <Child onClick={this.handleChildClick.bind(null,childData)} text={childData.childText}/>;
    }.bind(this));
    return <div>{children}</div>;
  },

  handleChildClick: function(childData,event) {
     alert("The Child button data is: " + childData.childText + " - " + childData.childNumber);
     alert("The Child HTML is: " + event.target.outerHTML);
  }
});

JsFiddle

It is also possible to use this.handleChildClick.bind(null,childIndex) and then use this.state.childrenData[childIndex]

Note we are binding with a null context because otherwise React issues a warning related to its autobinding system. Using null means you don't want to change the function context. See also.

About encapsulation and coupling in other answers

This is for me a bad idea in term of coupling and encapsulation:

var Parent = React.createClass({
  handleClick: function(childComponent) {
     // using childComponent.props
     // using childComponent.refs.button
     // or anything else using childComponent
  },
  render: function() {
    <Child onClick={this.handleClick} />
  }
});

Using props:
As I explained above, you already have the props in the parent so it's useless to pass the whole child component to access props.

Using refs:
You already have the click target in the event, and in most case this is enough.
Additionnally, you could have used a ref directly on the child:

<Child ref="theChild" .../>

And access the DOM node in the parent with

React.findDOMNode(this.refs.theChild)

For more advanced cases where you want to access multiple refs of the child in the parent, the child could pass all the dom nodes directly in the callback.

The component has an interface (props) and the parent should not assume anything about the inner working of the child, including its inner DOM structure or which DOM nodes it declares refs for. A parent using a ref of a child means that you tightly couple the 2 components.

To illustrate the issue, I'll take this quote about the Shadow DOM, that is used inside browsers to render things like sliders, scrollbars, video players...:

They created a boundary between what you, the Web developer can reach
and what’s considered implementation details, thus inaccessible to
you. The browser however, can traipse across this boundary at will.
With this boundary in place, they were able to build all HTML elements
using the same good-old Web technologies, out of the divs and spans
just like you would.

The problem is that if you let the child implementation details leak into the parent, you make it very hard to refactor the child without affecting the parent. This means as a library author (or as a browser editor with Shadow DOM) this is very dangerous because you let the client access too much, making it very hard to upgrade code without breaking retrocompatibility.

If Chrome had implemented its scrollbar letting the client access the inner dom nodes of that scrollbar, this means that the client may have the possibility to simply break that scrollbar, and that apps would break more easily when Chrome perform its auto-update after refactoring the scrollbar... Instead, they only give access to some safe things like customizing some parts of the scrollbar with CSS.

About using anything else

Passing the whole component in the callback is dangerous and may lead novice developers to do very weird things like calling childComponent.setState(...) or childComponent.forceUpdate(), or assigning it new variables, inside the parent, making the whole app much harder to reason about.

Edit: ES6 examples

As many people now use ES6, here are the same examples for ES6 syntax

The child can be very simple:

const Child = ({
  onClick, 
  text
}) => (
  <button onClick={onClick}>
    {text}
  </button>
)

The parent can be either a class (and it can eventually manage the state itself, but I'm passing it as props here:

class Parent1 extends React.Component {
  handleChildClick(childData,event) {
     alert("The Child button data is: " + childData.childText + " - " + childData.childNumber);
     alert("The Child HTML is: " + event.target.outerHTML);
  }
  render() {
    return (
      <div>
        {this.props.childrenData.map(child => (
          <Child
            key={child.childNumber}
            text={child.childText} 
            onClick={e => this.handleChildClick(child,e)}
          />
        ))}
      </div>
    );
  }
}

But it can also be simplified if it does not need to manage state:

const Parent2 = ({childrenData}) => (
  <div>
     {childrenData.map(child => (
       <Child
         key={child.childNumber}
         text={child.childText} 
         onClick={e => {
            alert("The Child button data is: " + child.childText + " - " + child.childNumber);
                    alert("The Child HTML is: " + e.target.outerHTML);
         }}
       />
     ))}
  </div>
)

JsFiddle

PERF WARNING (apply to ES5/ES6): if you are using PureComponent or shouldComponentUpdate, the above implementations will not be optimized by default because using onClick={e => doSomething()}, or binding directly during the render phase, because it will create a new function everytime the parent renders. If this is a perf bottleneck in your app, you can pass the data to the children, and reinject it inside "stable" callback (set on the parent class, and binded to this in class constructor) so that PureComponent optimization can kick in, or you can implement your own shouldComponentUpdate and ignore the callback in the props comparison check.

You can also use Recompose library, which provide higher order components to achieve fine-tuned optimisations:

// A component that is expensive to render
const ExpensiveComponent = ({ propA, propB }) => {...}

// Optimized version of same component, using shallow comparison of props
// Same effect as React's PureRenderMixin
const OptimizedComponent = pure(ExpensiveComponent)

// Even more optimized: only updates if specific prop keys have changed
const HyperOptimizedComponent = onlyUpdateForKeys(['propA', 'propB'])(ExpensiveComponent)

In this case you could optimize the Child component by using:

const OptimizedChild = onlyUpdateForKeys(['text'])(Child)

passing props form child to parent component in react

You can't pass props from child to parent in React, it's only one way (from parent to child).

You should either:

Put the state in the parent component and manipulate it from the child component by passing the setter function in the props
Use something like Redux Toolkit to create a global state that all components can have access to

React cannot pass props to parent component

You can set up a data state in your app component using a useState hook and pass a reference to a setter function which modifies your data and set it to a value and pass both of them to the Register component. Also, pass the data to your chat component as you would need it. You can try like below,

In App component,

...

function App(props) {
  const [data,setData] = useState('');

  const myDataSetterFunction = (dataToBeSet) => {
     setData(dataToBeSet);
  }

  return (
    <BrowserRouter>
      <Routes>
        <Route path="/" element={<Register intialData={data} myDataSetterFunction={myDataSetterFunction}   />}>

          <Route
            path="chat"
            element={(props) => <Chat dataToBeSupplied={data} {...props} data={true} />}
          />
        </Route>
        <Route

....

The Register component can modify the data and use the passed setter Function to modify the state of the hook. As soon as the data is modified there will be a re-render triggered which will pass the data or you can pass the data only if the data changes from the initial value to be more safer.

Inside the Register.js use the props to call the function passed to set the data inside the app doing something like this.

props.myDataSetterFunction( ...dataToBeReturned... );

Also, Remember to make sure the data has some value before passing it to the chat and using it.

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

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.

See the code comment why I don't recommend this approach.

const Child = ({ childName, sayHello }) => (
  <button onClick={() => sayHello(childName)}>{childName}</button>
);

function Parent({ children }) {
  // We clone and pass this `sayHello` function
  // into the child elements.
  function sayHello(childName) {
    console.log(`Hello from ${childName} the child`);
  }

  const childrenWithProps = React.Children.map(children, child => {
    // Checking isValidElement is the safe way and avoids a
    // typescript error too.
    if (React.isValidElement(child)) {
      return React.cloneElement(child, { sayHello });
    }
    return child;
  });

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

function App() {
  // This approach is less type-safe and Typescript friendly since it
  // looks like you're trying to render `Child` with `sayHello` missing.
  // It's also confusing to readers of this code.
  return (
    <Parent>
      <Child childName="Billy" />
      <Child childName="Bob" />
    </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>

Pass Props to Parent Component in React.Js