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Possible Plagiarism

Plagiarized on 2019-08-02
by Gergő Mészáros

Original Post

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



            
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It would be better to see you full code but you want something like this:

<!-- begin snippet: js hide: false console: true babel: true -->
<!-- language: lang-js -->
class Icecream extends React.Component { // this is the state you modify, every time you change it // render() will run state = { icecreams: [], }; // take all the elements from the current array and the new one // and store it in the state -> trigger render() addIceCream = newIcecream => this.setState(state => ({ icecreams: [...state.icecreams, newIcecream], })); // remove the item with the given index and store // the result in the state -> trigger render removeIcecream = iceCreamIndex => this.setState(state => { const newIcecreams = [...state.icecreams]; newIcecreams.splice(iceCreamIndex, 1); return { icecreams: newIcecreams, } }); render() { // instead of this you can do this.addIceCream etc. const { addIceCream, removeIcecream } = this; const { icecreams } = this.state; return ( <div> <button onClick={() => addIceCream(`Icream ${icecreams.length + 1}`) } > add icecream </button> <ul> {icecreams.map((item, index) => ( <li> {item} <button onClick={() => removeIcecream(index)}> remove </button> </li> ))} </ul> </div> ); } };
ReactDOM.render(<Icecream />, document.getElementById('app'));
<!-- language: lang-html -->
<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> <div id="app"></div>
<!-- end snippet -->

That's *property spread notation*. It was added in ES2018, but long-supported in React projects via transpilation (as "JSX spread attributes" even though you could do it elsewhere, too, not just attributes).
`{...this.props}` *spreads out* the "own" 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://reactjs.org/docs/jsx-in-depth.html#children-in-jsx

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