Duvida com JSON.parse

let idPlano = document.querySelector('input[name="planoRadio"]:checked').value;
var oReq = new XMLHttpRequest();
oReq.onload = planosListener;
oReq.open("get", "http://192.168.1.4:3000/planos/"+ idPlano, true);
oReq.send();
console.log("4");
var nomePlano = '';

function planosListener () {
    console.log("1");
    let planos = JSON.parse(this.responseText);
    nomePlano = planos[0];
    console.log(nomePlano.Nome);
    return nomePlano;
};
console.log(nomePlano.nome);