“SyntaxError: Unexpected token < in JSON at position 0”

Question

In a React app component which handles Facebook-like content feeds, I am running into an error:

Feed.js:94 undefined \"parsererror\" \"SyntaxError: Un

Answer 1

If anyone else is using fetch from the "Using Fetch" documentation on Web API's in Mozilla: (This is really useful: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch)

  fetch(api_url + '/database', {
    method: 'POST', // or 'PUT'
    headers: {
     'Content-Type': 'application/json'
    },
    body: qrdata //notice that it is not qr but qrdata
  })
  .then((response) => response.json())
  .then((data) => {
    console.log('Success:', data);
  })  
  .catch((error) => {
  console.error('Error:', error);  });

This was inside the function:

async function postQRData(qr) {

  let qrdata = qr; //this was added to fix it!
  //then fetch was here
}

I was passing into my function qr what I believed to be an object because qr looked like this: {"name": "Jade", "lname": "Bet", "pet":"cat"} but I kept getting syntax errors. When I assigned it to something else: let qrdata = qr; it worked.

Answer 2

Just to add to the answers, it also happens when your API response includes

<?php{username: 'Some'}

which could be a case when your backend is using PHP.

Answer 3

In my case (backend), I was using res.send(token);

Everything got fixed when I changed to res.send(data);

You may want to check this if everything is working and posting as intended, but the error keeps popping up in your front-end.

Answer 4

i was facing the same issue
i removed the dataType:'json' from the $.ajax method

Answer 5

Protip: Testing json on a local Node.js server? Make sure you don't already have something routing to that path

'/:url(app|assets|stuff|etc)';

Answer 6

This error occurs when you define the response as application/json and you are getting a HTML as a response. Basically, this happened when you are writing server side script for specific url with a response of JSON but the error format is in HTML.