How can I update the parent's state in React?

Solution 1:

For child-parent communication you should pass a function setting the state from parent to child, like this

class Parent extends React.Component {
  constructor(props) {
    super(props)

    this.handler = this.handler.bind(this)
  }

  handler() {
    this.setState({
      someVar: 'some value'
    })
  }

  render() {
    return <Child handler = {this.handler} />
  }
}

class Child extends React.Component {
  render() {
    return <Button onClick = {this.props.handler}/ >
  }
}

This way the child can update the parent's state with the call of a function passed with props.

But you will have to rethink your components' structure, because as I understand components 5 and 3 are not related.

One possible solution is to wrap them in a higher level component which will contain the state of both component 1 and 3. This component will set the lower level state through props.

Solution 2:

I found the following working solution to pass the onClick function argument from the child to the parent component:

Version with passing a method()

//ChildB component
class ChildB extends React.Component {

    render() {

        var handleToUpdate = this.props.handleToUpdate;
        return (<div><button onClick={() => handleToUpdate('someVar')}>
            Push me
          </button>
        </div>)
    }
}

//ParentA component
class ParentA extends React.Component {

    constructor(props) {
        super(props);
        var handleToUpdate = this.handleToUpdate.bind(this);
        var arg1 = '';
    }

    handleToUpdate(someArg){
        alert('We pass argument from Child to Parent: ' + someArg);
        this.setState({arg1:someArg});
    }

    render() {
        var handleToUpdate = this.handleToUpdate;

        return (<div>
                    <ChildB handleToUpdate = {handleToUpdate.bind(this)} /></div>)
    }
}

if(document.querySelector("#demo")){
    ReactDOM.render(
        <ParentA />,
        document.querySelector("#demo")
    );
}

Look at JSFiddle

Version with passing an Arrow function

//ChildB component
class ChildB extends React.Component {

    render() {

        var handleToUpdate = this.props.handleToUpdate;
        return (<div>
          <button onClick={() => handleToUpdate('someVar')}>
            Push me
          </button>
        </div>)
    }
}

//ParentA component
class ParentA extends React.Component {
    constructor(props) {
        super(props);
    }

    handleToUpdate = (someArg) => {
            alert('We pass argument from Child to Parent: ' + someArg);
    }

    render() {
        return (<div>
            <ChildB handleToUpdate = {this.handleToUpdate} /></div>)
    }
}

if(document.querySelector("#demo")){
    ReactDOM.render(
        <ParentA />,
        document.querySelector("#demo")
    );
}

Look at JSFiddle

Solution 3:

This is how we can do it with the new useState hook. Method - Pass the state changer function as a props to the child component and do whatever you want to do with the function

import React, {useState} from 'react';

const ParentComponent = () => {
  const[state, setState]=useState('');
  
  return(
    <ChildConmponent stateChanger={setState} />
  )
}


const ChildConmponent = ({stateChanger, ...rest}) => {
  return(
    <button onClick={() => stateChanger('New data')}></button>
  )
}