React: setInterval

import React from 'react';
import "./Ticker.css";


export default class Ticker extends React.Component {


updateExchangeRatio = () => {
console.log(this.state.valcur);
return fetch("https://min-api.cryptocompare.com/data/price?fsym="+this.state.valcur[0]+"&tsyms=USD").then(r => r.json()).then(res => {this.setState({value:  res.USD})});
}

constructor(props){
super(props);
this.state = {
value: 0,
valcur:this.props.pair.toUpperCase().split("_")
}
}

componentDidMount(){
this.updateExchangeRatio();
this.interval = setInterval(this.updateExchangeRatio, 30000);
}

componentWillUnmount(){
clearInterval(this.interval);
}

render(){
const { pair } = this.props;
return (
<div className="ticker">
<p>{pair.toUpperCase().replace('_', ' to ')}</p>
<p>{this.state.value}</p>
</div>
)
}

}