You can add an additional state variable `isActive` that keeps track of if your timer is active or not and choose what function to call when clicking the button based on that.
**Example**
<!-- begin snippet: js hide: false console: true babel: true -->
<!-- language: lang-js -->
class Timer extends React.Component {
state = {
isActive: false,
secondsElapsed: 1800000 / 1000 //time in seconds
};
getHours() {
return ("0" + Math.floor(this.state.secondsElapsed / 3600)).slice(-2);
}
getMinutes() {
return ("0" + Math.floor((this.state.secondsElapsed % 3600) / 60)).slice(
-2
);
}
getSeconds() {
return ("0" + (this.state.secondsElapsed % 60)).slice(-2);
}
startTime = () => {
this.countdown = setInterval(() => {
this.setState(({ secondsElapsed }) => ({
isActive: true,
secondsElapsed: secondsElapsed - 1
}));
}, 1000);
};
resetTime = () => {
this.setState({
secondsElapsed: 1800000 / 1000,
isActive: false
});
};
pauseTime = () => {
clearInterval(this.countdown);
this.setState({ isActive: false });
};
render() {
return (
<div className="App">
<div className="timer-container">
<span className="bloc-timer"> {this.getHours()}</span>
<span className="bloc-timer"> :{this.getMinutes()}</span>
<span className="bloc-timer"> :{this.getSeconds()}</span>
</div>
<div>
<button
onClick={this.state.isActive ? this.pauseTime : this.startTime}
>
Start/Pause
</button>
<button onClick={this.resetTime}>Reset</button>
</div>
</div>
);
}
}
ReactDOM.render(<Timer />, 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>
<!-- 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 — the good kind — 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 — 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
