SyntaxError: Unexpected token o in JSON at position 1

I'm parsing some data using a type class in my controller. I'm getting data as follows:

{  
   "data":{  
      "userList":[  
         {  
            "id":1,
            "name":"soni"
         }
      ]
   },
   "status":200,
   "config":{  
      "method":"POST",
      "transformRequest":[  
         null
      ],
      "transformResponse":[  
         null
      ],
      "url":"/home/main/module/userlist",
      "headers":{  
         "rt":"ajax",
         "Tenant":"Id:null",
         "Access-Handler":"Authorization:null",
         "Accept":"application/json, text/plain, */*"
      }
   },
   "statusText":"OK"
}

I tried to store the data like this

var userData = _data;
var newData = JSON.parse(userData).data.userList;

How can I extract the user list to a new variable?

The JSON you posted looks fine, however in your code, it is most likely not a JSON string anymore, but already a JavaScript object. This means, no more parsing is necessary.

You can test this yourself, e.g. in Chrome's console:

new Object().toString()
// "[object Object]"

JSON.parse(new Object())
// Uncaught SyntaxError: Unexpected token o in JSON at position 1

JSON.parse("[object Object]")
// Uncaught SyntaxError: Unexpected token o in JSON at position 1

JSON.parse() converts the input into a string. The toString() method of JavaScript objects by default returns [object Object], resulting in the observed behavior.

Try the following instead:

var newData = userData.data.userList;

The first parameter of the JSON.parse function is expected to be a string, and your data is a JavaScript object, so it will coerce it to the string "[object Object]". You should use JSON.stringify before passing the data:

JSON.parse(JSON.stringify(userData))

Don't ever use JSON.parse without wrapping it in try-catch block:

// payload 
let userData = null;

try {
	// Parse a JSON
	userData = JSON.parse(payload);	
} catch (e) {
	// You can read e for more info
	// Let's assume the error is that we already have parsed the payload
	// So just return that
	userData = payload;
}

// Now userData is the parsed result

Just above JSON.parse, use:

var newData = JSON.stringify(userData)

We can also add checks like this:

function parseData(data) {
    if (!data) return {};
    if (typeof data === 'object') return data;
    if (typeof data === 'string') return JSON.parse(data);

    return {};
}

You can simply check the typeof userData & JSON.parse() it only if it's string:

var userData = _data;
var newData;
if (typeof userData === 'object')
  newData = userData.data.userList; // dont parse if its object
else if (typeof userData === 'string')
  newData = JSON.parse(userData).data.userList; // parse if its string

Unexpected 'O' error is thrown when JSON data or String happens to get parsed.

If it's string, it's already stringfied. Parsing ends up with Unexpected 'O' error.

I faced similar( although in different context), I solved the following error by removing JSON Producer.

    @POST
	@Produces({ **MediaType.APPLICATION_JSON**})
	public Response login(@QueryParam("agentID") String agentID , Officer aOffcr ) {
      return Response.status(200).entity("OK").build();
     
  }

The response contains "OK" string return. The annotation marked as @Produces({ MediaType.APPLICATION_JSON}) tries to parse the string to JSON format which results in Unexpected 'O'.

Removing @Produces({ MediaType.APPLICATION_JSON}) works fine. Output : OK

Beware: Also, on client side, if you make ajax request and use JSON.parse("OK"), it throws Unexpected token 'O'

O is the first letter of the string

JSON.parse(object) compares with jQuery.parseJSON(object);

JSON.parse('{ "name":"Yergalem", "city":"Dover"}'); --- Works Fine

Give a try catch like this, this will parse it if its stringified or else will take the default value

let example;
   try {
   example  = JSON.parse(data)
  } catch(e) {
    example = data
  }

First set request value in variable like:

let reqData = req.body.reqData;
if (reqData) {
  let reqDataValue = JSON.parse(JSON.stringify(reqData));
}