how to handle values other than json in fetch api call

I want to send json data to API AND GET A STRING VALUE WILL IT BE POSSIBLE 

I have a node js API which return a value(not json type):

res.send(code);

in reactjs i am using fetch api in the following way,

  const options = {
  method: "POST",
  headers: {
    "Content-Type": "application/json"

  },
  body: JSON.stringify({ url: this.state.url })
};

fetch("http://localhost:3000/messages", options)
  .then(response => response)
  .then(data => {
    console.log(data)
    this.setState({ code: data.code });
  });

but i am getting an error as

localhost/:1 Uncaught (in promise) SyntaxError: Unexpected token h in JSON at position 0

i know i am getting this error as i am not passing json from the api can u help me solve this error the code in node api

        const express = require("express");
          const app = express();
         const cors = require("cors");
            const shorten = require("../../task1/src/shorten");
          const fs = require("fs");
           app.use(cors()); // to send CORS headers.
             app.use(express.urlencoded()); 
            app.use(express.json()); // to support JSON-encoded bodies.
           const fileName = "urldata.json";

             var write = (shortcode, urlData, url) => {
                 console.log(shortcode + ":::in writing");
                var shortcode = shortcode;
                  urlData.urlcodes.push({
                          url: url,
                      shorten: shortcode
                            });

           fs.writeFileSync(fileName, JSON.stringify(urlData), (err, data) 
        => {
          if (err) console.log(err);
          console.log("written in bdy");
             });
             };

                  var filecheck = (urlData, url, shrtcd) => {
                   {
             if (!shrtcd) {
  shortcode = shorten(url);
  write(shortcode, urlData, url);
  return shortcode;
     } else {
  write(shrtcd, urlData, url);

  return shrtcd;
        }
      }

          for (var i = 0; i < urlData["urlcodes"].length; i++) {
if (urlData["urlcodes"][i].url === url) {
  shortcode = urlData["urlcodes"][i].shorten;
  return shortcode;
            } else continue;
            }
         };

       app.post("/shortcodes", function(req, res) {

          console.log(req.body)
              if (!fs.existsSync(fileName)) {
                 const data = { urlcodes: [] };
                fs.createWriteStream(fileName, "utf-8");
                  fs.writeFile(fileName, JSON.stringify(data), err => {
                        console.log(err);
                       });
                          }
             fs.readFile(fileName, "utf-8", (err, data) => {
                if (err) console.log(err);
              var urlData = JSON.parse(data);

              var code = filecheck(urlData, req.body.url, req.body.shortcode);

          res.send(code); 
                });
               });