“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

This might be old. But, it just occurred in angular, the content type for request and response were different in my code. So, check headers for ,

 let headers = new Headers({
        'Content-Type': 'application/json',
        **Accept**: 'application/json'
    });

in React axios

axios({
  method:'get',
  url:'http://  ',
 headers: {
         'Content-Type': 'application/json',
        Accept: 'application/json'
    },
  responseType:'json'
})

jQuery Ajax:

 $.ajax({
      url: this.props.url,
      dataType: 'json',
**headers: { 
          'Content-Type': 'application/json',
        Accept: 'application/json'
    },**
      cache: false,
      success: function (data) {
        this.setState({ data: data });
      }.bind(this),
      error: function (xhr, status, err) {
        console.error(this.props.url, status, err.toString());
      }.bind(this)
    });
  },

Answer 2

just something basic to check, make sure you dont have anything commented out in the json file

//comments here will not be parsed and throw error

Answer 3

The possibilities for this error are overwhelming.

In my case, I found that the issue was adding the homepage filed in package.json caused the issue.

Worth checking: in package.json change:

homepage: "www.example.com"

to

hompage: ""   

Answer 4

In my case, I was getting this running webpack, and it turned out to be some corruption somewhere in the local node_modules dir.

rm -rf node_modules
npm install

...was enough to get it working right again.

Answer 5

For me, this happened when one of the properties on the object I was returning as JSON threw an exception.

public Dictionary<string, int> Clients { get; set; }
public int CRCount
{
    get
    {
        var count = 0;
        //throws when Clients is null
        foreach (var c in Clients) {
            count += c.Value;
        }
        return count;
    }
}

Adding a null check, fixed it for me:

public Dictionary<string, int> Clients { get; set; }
public int CRCount
{
    get
    {
        var count = 0;
        if (Clients != null) {
            foreach (var c in Clients) {
                count += c.Value;
            }
        }
        return count;
    }
}

Answer 6

This might cause due to your javascript code is looking at some json response and you received something else like text.