Add key to the <Block/> Component
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<!-- language: lang-js -->
class App extends React.Component {
state = {
comments: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
};
addNumbers = () => {
var comments = this.state.comments;
var commentsLength = this.state.comments.length;
comments.unshift(commentsLength);
this.setState({ comments });
};
render() {
return (
<div>
<p
style={{
marginLeft: 20,
background: "royalblue",
width: 130,
color: "white",
padding: "10px 20px",
textAlign: "center",
borderRadius: 10,
cursor: "pointer"
}}
onClick={this.addNumbers.bind(this)}
>
Add Block
</p>
{this.state.comments.map(single => (
<Block key={single} singleDigit={single} />
))}
</div>
);
}
}
class Block extends React.Component {
state = {
showMessage: false
};
render() {
return (
<div style={{ paddingLeft: 20, paddingRight: 20, paddingTop: 10 }}>
<div
style={{
border: "2px solid rgba(0,0,0,0.2)",
borderRadius: 10,
height: 70,
padding: 10
}}
>
<div style={{ display: "flex", justifyContent: "space-around" }}>
<div>{this.props.singleDigit}</div>
<div
style={{ cursor: "pointer" }}
onClick={() => {
this.setState({ showMessage: true });
}}
>
Show Message
</div>
</div>
{this.state.showMessage && <h3>HERE IS THE MESSAGE</h3>}
</div>
<div />
</div>
);
}
}
ReactDOM.render(<App />, 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"></div>
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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 — the good kind — for putting a `children` property in the opening tag. Example:
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<!-- 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>
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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 — 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;
}
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[1]: https://reactjs.org/docs/jsx-in-depth.html#children-in-jsx
