app.post pass objects from express server to html?

Question

how do I pass objects from server to html?

I have my nodejs code here below that I stripped off details to keep it simple.

nodejs.js

const bodyParser = require('body-parser');
const urlencodedParser = bodyParser.urlencoded({ extended: false })
app.use(bodyParser.json());

app.post('/',urlencodedParser, function(req, res) {
  Object = new Class();
  res.status(200).json(Object);
});

Here is my js code called by html.

myjs.js

function fetcher() {
    fetch('/',
      {
        method: "POST",
        body: JSON.stringify({"name": document.getElementById("name").value}),
        headers: { "Content-Type": "application/json" }
        }
    )
    .then(function(response) {
      return response.json();
    })
    .then(function(Obj) {
         console.log(obj.func());
    });
  }

Answer 1

1. The body-parser package is redundant. All the previous middleware is available in Express already via express.json(), express.urlencoded(), etc.
2. If you're expecting a JSON request body, don't use the urlencoded middleware directly in your route handler.
3. Object is a reserved word. You should not name any variables or symbols (classes, functions, etc) using it
4. In order to respond with JSON, whatever object you're passing needs to be serialisable. This can be customised via a toJSON() method.

class SomeClass {
  constructor(name) {
    this.name = name;
  }

  // customise JSON serialisation
  toJSON() {
    return { name: this.name };
  }
}

app.use(express.json());

app.post("/", (req, res) => {
  const obj = new SomeClass(req.body.name);
  res.json(obj); // no need for `status(200)`, it's implied
});

---

On the client-side, JSON is a string format. Functions and methods cannot be represented. All you will have is data

fetch("/", {
  method: "POST",
  body: JSON.stringify({ name: document.getElementById("name").value }),
  headers: { "Content-Type": "application/json" },
})
  .then((res) => (res.ok ? res.json() : Promise.reject(res)))
  .then((obj) => {
    console.log(obj); // no `.func()` here
  })
  .catch(console.error);

See also How to store a javascript function in JSON