cep.axios.express.js

const express = require( 'express' )
const axios = require( 'axios' )
const app = express()

const isCepValid = ( cep ) => 
  ( cep.length < 8 || cep.length > 9 )
    ? new Error( 'Cep inválido' )
    : true

const sanitizeCEP = ( cep ) => cep.replace( /\D/g, '' )

const getCEP = ( req, res ) => {
  const codeFormated = sanitizeCEP( req.query.code )

  if ( isCepValid( codeFormated ) instanceof Error ) {
    res.status( 400 )
    return res.send( 'Cep inválido' )
  }

  axios.get( 'https://viacep.com.br/ws/' + codeFormated + '/json' )
    .then( function ( response ) {
      console.log( response )
      res.json( response.data )
    } )
    .catch( function ( error ) {
      console.log( error )
    } )
}

app.get( '/cep', getCEP )

app.listen( 9000 )
console.log( 'Server started! At http://localhost:9000' )