Usando uma API de Ceps

challenge-28.js

(function(win, doc){
  'use strict';

  let formAdress = {
    cep: doc.querySelector('[data-js="cep"]'),
    state: doc.querySelector('[data-js="state"]'),
    city: doc.querySelector('[data-js="city"]'),
    street: doc.querySelector('[data-js="street"]'),
    district: doc.querySelector('[data-js="district"]')
  }

  let $button = doc.querySelector('[data-js="button"]');
  let adressInfo;
  let cep;

  $button.addEventListener('click', function(event){
    event.preventDefault();
    getAdress(formAdress.cep.value);
    setTimeout(() => {
      console.log(showAdress());
    }, 1000);
  });

  function getAdress (url) {
    let conection = new XMLHttpRequest();
    conection.open('get', 'http://apps.widenet.com.br/busca-cep/api/cep/'+ url.match(/\d/g) +'.json');
    conection.addEventListener('readystatechange', ()=> {
    if(isRequestOk(conection))
      adressInfo = JSON.parse(conection.responseText);
    });
    conection.send();
  }

  function isRequestOk (conection) {
    return conection.readyState === 4 && conection.status === 200;
  }

  function showAdress() {
    if(adressInfo.status === 0)
      return adressInfo.message;

    formAdress.state.value = adressInfo.state;
    formAdress.city.value = adressInfo.city;
    formAdress.street.value = adressInfo.address;
    formAdress.district.value = adressInfo.district;
  }


}(window, document));