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Possible Plagiarism

Plagiarized on 2020-05-24
by CanUver

Original Post

Original - Posted on 2015-06-25
by T.J. Crowder



            
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Welcome Stack Overflow! To send data from the child component to the parent component, you must type a function in the parent component and send it to the child component as a props first. you can then take these props in the subcomponent and send values into it, and then use them as you wish in the main component and manage your application.
You'll see what the example I've prepared here is like.
<!-- begin snippet: js hide: false console: true babel: true -->
<!-- language: lang-js -->
//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") ); }
<!-- language: lang-html -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.0/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.0/umd/react-dom.production.min.js"></script>
<div id="demo">134</div>
<!-- end snippet -->

That's [*property spread notation*][1]. It was added in ES2018 (spread for arrays/iterables was earlier, ES2015), but it's been supported in React projects for a long time via transpilation (as "[JSX spread attributes][2]" even though you could do it elsewhere, too, not just attributes).
`{...this.props}` *spreads out* the "own" enumerable properties in `props` as discrete properties on the `Modal` element you're creating. For instance, if `this.props` contained `a: 1` and `b: 2`, then
<Modal {...this.props} title='Modal heading' animation={false}>
would be the same as
<Modal a={this.props.a} b={this.props.b} title='Modal heading' animation={false}>
But it's dynamic, so whatever "own" properties are in `props` are included.
Since `children` is an "own" property in `props`, spread will include it. So if the component where this appears had child elements, they'll be passed on to `Modal`. Putting child elements between the opening tag and closing tags is just syntactic sugar&nbsp;&mdash; the good kind&nbsp;&mdash; for putting a `children` property in the opening tag. Example:
<!-- begin snippet: js hide: true console: true babel: true -->
<!-- language: lang-js -->
class Example extends React.Component { render() { const { className, children } = this.props; return ( <div className={className}> {children} </div> ); } } ReactDOM.render( [ <Example className="first"> <span>Child in first</span> </Example>, <Example className="second" children={<span>Child in second</span>} /> ], document.getElementById("root") );
<!-- language: lang-css -->
.first { color: green; } .second { color: blue; }
<!-- language: lang-html -->
<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<!-- end snippet -->
Spread notation is handy not only for that use case, but for creating a new object with most (or all) of the properties of an existing object&nbsp;&mdash; which comes up a lot when you're updating state, since you can't modify state directly:
this.setState(prevState => { return {foo: {...prevState.foo, a: "updated"}}; });
That replaces `this.state.foo` with a new object with all the same properties as `foo` except the `a` property, which becomes `"updated"`:
<!-- begin snippet: js hide: true console: true babel: false -->
<!-- language: lang-js -->
const obj = { foo: { a: 1, b: 2, c: 3 } }; console.log("original", obj.foo); // Creates a NEW object and assigns it to `obj.foo` obj.foo = {...obj.foo, a: "updated"}; console.log("updated", obj.foo);

<!-- language: lang-css -->
.as-console-wrapper { max-height: 100% !important; }
<!-- end snippet -->

[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax [2]: https://reactjs.org/docs/jsx-in-depth.html#spread-attributes

        
Present in both answers; Present only in the new answer; Present only in the old answer;