0
The error appears in this.converter = this.converter.bind(this);
My script:
import React, { Component } from 'react'
export default class conversor extends Component {
    
    constructor(props){
        super(props);
        this.state = {
            moedaA_valor: "",
            moedaB_valor: 0,
        }
    }
        this.converter = this.converter.bind(this);
    converter(){
        let de_para = `${this.props.moedaA}_${this.props.moedaB}`;
        let url = `https://api.currconv.com/api/v7/convert?q=${de_para}&compact`
        fetch(url)
        .then(res=>{
            return res.json()
        })
        .then(json=>{
            let cotacao = json[de_para].val;
            let moedaB_valor = ( parseFloat (this.state.moedaA_valor) * cotacao).toFixed(2)
            this.setState({moedaB_valor})
        })
    }
    
    render() {
        return(
            <div className="conversor">
                <h2>{this.props.moedaA} para {this.props.moedaB}</h2> 
                <input type="text" onChange={(event)=>(this.setState({moedaA_valor:event.target.value}))}></input>
                <input type="button" onClick= {this.converter} value="Converter"></input>
                <h2>{this.state.moedaB_valor}</h2>               
            </div>
        )
    }
}
Pedro, can you edit with the full code of your class? Furthermore, I think it is pq vc can not put commands in the middle of the class, the commands must exist inside a method.
– Allan Juan