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Possible Plagiarism

Plagiarized on 2020-02-13
by CertainPerformance

Original Post

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



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

`Object.assign` will assign own enumerable properties from all arguments 2nd and above into the object in the 1st argument. So
``` editingProfile: Object.assign(profileInitialState, this.props.profile) ```
*mutates* `profileInitialState`. As a result, the second time that line runs, results from the first may still exist in `profileInitialState`.
Instead, use
``` editingProfile: Object.assign({}, profileInitialState, this.props.profile) ```
to create an entirely new object:
<!-- begin snippet: js hide: true console: true babel: true -->
<!-- language: lang-js -->
const profileInitialState = { name: '', title: '', headline: '', bio: '' }
class Bio extends React.Component { constructor(props) { super(props); this.state = { editingProfile: Object.assign({}, profileInitialState, this.props.profile) } } render() { const { profile } = this.props; const { editingProfile } = this.state; console.log(profile); // props profile has correct info console.log(editingProfile); // state profile takes on old values return ( <div> <h1>{editingProfile.name}</h1> <h2>{editingProfile.title}</h2> <h3>{editingProfile.headline}</h3> <p>{editingProfile.bio}</p> </div> ); } }
const newProfile = { name: 'Test 1', title: 'Title 1', headline: 'Headline 1', bio: 'Bio 1' }
const legacyProfile = { name: 'Test 2', title: 'Title 2', bio: 'Bio 2' }
ReactDOM.render( <React.Fragment> <Bio profile={newProfile} /> <Bio profile={legacyProfile} /> </React.Fragment>, document.getElementById('root') );
<!-- 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="root"> <!-- This element's contents will be replaced with your component. --> </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 along 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;