Passing input value to sibling through parent - reactjs

Question

I'm trying to pass input value from one child to another child using setState. It renders the first element, but not the second element in the first child...
class App extends Component {
constructor(props) {
super(props);
this.state = {};
};
showTekst = () => {
const inpValue = document.querySelector('.inpValue').value;
this.setState({
name: 'Bruce Wayne',
namefromvalue: inpValue.value
});
}
render() {
return (
<div className="app">
<Button showTekst={this.showTekst.bind(this)} />
<Text name={this.state.name} namefromvalue={this.state.namefromvalue}/>
<Inputvalue />
</div>
);
}
}
ReactDOM.render(<App />, document.getElementById('root'));
class Inputvalue extends Component {
render() {
return (
<input className="inpValue"></input>
);
}
}
class Text extends Component {
render() {
return (
<div>
<h1>This is text..</h1>
<h2>{this.props.namefromvalue}</h2>
<p>{this.props.name}</p>
</div>
);
}
}

Answer 1

If you want to show the text from the Inputvalue component in the Text component only when the Button component is clicked you can store the input value in the App instance and update the App state when the Button is clicked.
To do so, we define an onChange prop in the Inputvalue component so that every time the text in the input changes, the prop is called with the new value. With that prop we update the value in the App instance. This value will always be in sync with the input value.
Last, when the button is clicked we update the App state with the input value so that the Text component renders its value.
class App extends Component {
constructor(props) {
super(props);
this.state = {};
// This variable will hold the input value.
this.inputValue = "";
}
showTekst = () => {
// Update with the current input value.
this.setState({
name: "Bruce Wayne",
namefromvalue: this.inputValue
});
};
onInputChange = value => {
// Update the input value.
this.inputValue = value;
};
render() {
return (
<div className="app">
<Button showTekst={this.showTekst.bind(this)} />
<Text name={this.state.name} namefromvalue={this.state.namefromvalue} />
<Inputvalue onChange={this.onInputChange} />
</div>
);
}
}
ReactDOM.render(<App />, document.getElementById('root'));
class Button extends Component {
render() {
return <button onClick={this.props.showTekst}>Show text</button>;
}
}
class Inputvalue extends Component {
render() {
return (
<input
className="inpValue"
onChange={ev => this.props.onChange(ev.target.value)}
/>
);
}
}
class Text extends Component {
render() {
return (
<div>
<h1>This is text..</h1>
<h2>{this.props.namefromvalue}</h2>
<p>{this.props.name}</p>
</div>
);
}
}