passing parent ref to child props in react code example

Example 1: react pass prop to parent

//Form (Parent)
import React, { useState, Component } from 'react';
import Input from '../../shared/input-box/InputBox'

const Form = function (props) {

    const [value, setValue] = useState('');

    const onchange = (data) => {
        setValue(data)
        console.log("Form>", data);
    }

    return (
        <div>
            <Input data={value} onchange={(e) => { onchange(e) }}/>
        </div>
    );
}
export default Form;

//Input Box (Child)
import React from 'react';

const Input = function (props) {
    console.log("Props in Input :", props);

    const handleChange = event => {
        props.onchange(event.target.value);
    }

    return (
        <div>
            <input placeholder="name"
                id="name"
                onChange= {handleChange}
            />
        </div>
    );
}
export default Input;

Example 2: pass element from child to parent react

Parent:

<div className="col-sm-9">
     <SelectLanguage onSelectLanguage={this.handleLanguage} /> 
</div>

Child:

handleLangChange = () => {
    var lang = this.dropdown.value;
    this.props.onSelectLanguage(lang);            
}

Example 3: how to pass props from child to parent

class ToDoList extends React.Component {    constructor(props) {        super(props);        this.state = {            listDataFromChild: null        };        },    myCallback = (dataFromChild) => {        this.setState({ listDataFromChild: dataFromChild });    },    otherFn = () => {        [...within this other function now I still have access to this.state.listDataFromChild...]    }    render() {        return (            <div>                 <ToDoItem callbackFromParent={this.myCallback}/>                 [...now here I can pass this.state.listDataFromChild as a prop to any other child component...]                   </div>        );    }});

Example 4: use ref call parent component to child react

const { forwardRef, useRef, useImperativeHandle } = React;

// We need to wrap component in `forwardRef` in order to gain
// access to the ref object that is assigned using the `ref` prop.
// This ref is passed as the second parameter to the function component.
const Child = forwardRef((props, ref) => {

  // The component instance will be extended
  // with whatever you return from the callback passed
  // as the second argument
  useImperativeHandle(ref, () => ({

    getAlert() {
      alert("getAlert from Child");
    }

  }));

  return <h1>Hi</h1>;
});

const Parent = () => {
  // In order to gain access to the child component instance,
  // you need to assign it to a `ref`, so we call `useRef()` to get one
  const childRef = useRef();

  return (
    <div>
      <Child ref={childRef} />
      <button onClick={() => childRef.current.getAlert()}>Click</button>
    </div>
  );
};

ReactDOM.render(
  <Parent />,
  document.getElementById('root')
);