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The "Unexpected token u in JSON at position 0" error occurs when we pass an undefined value to the JSON. parse or $. parseJSON methods. To solve the error, inspect the value you're trying to parse and make sure it's a valid JSON string before parsing it.
The "Unexpected token u in JSON at position 0" is a typically Javascript error that will show up in your console log if the client has been directed to execute JSON. parse() on a string beginning with u instead of a stringified object. "u" is typically a stringified version of the undefined primitive.
This error can occur for a number of reasons, but is typically caused by a typo or incorrect code. Luckily, the SyntaxError: Unexpected token error is relatively easy to fix. In most cases, the error can be resolved by checking the code for accuracy and correcting any mistakes.
“Unexpected token < in JSON at position 0” is one of the fault which users have perceived in the bulk at the time of operations as similar to as a software developer. Quite often which happens in a situation while fetch function is used for sending an API request from a client.
The wording of the error message corresponds to what you get from Google Chrome when you run JSON.parse('<...'). I know you said the server is setting Content-Type:application/json, but I am led to believe the response body is actually HTML.
Feed.js:94 undefined "parsererror" "SyntaxError: Unexpected token < in JSON at position 0"with the line
console.error(this.props.url, status, err.toString())underlined.
The err was actually thrown within jQuery, and passed to you as a variable err. The reason that line is underlined is simply because that is where you are logging it.
I would suggest that you add to your logging. Looking at the actual xhr (XMLHttpRequest) properties to learn more about the response. Try adding console.warn(xhr.responseText) and you will most likely see the HTML that is being received.
You're receiving HTML (or XML) back from the server, but the dataType: json is telling jQuery to parse as JSON. Check the "Network" tab in Chrome dev tools to see contents of the server's response.
This ended up being a permissions problem for me. I was trying to access a url I didn't have authorization for with cancan, so the url was switched to users/sign_in. the redirected url responds to html, not json. The first character in a html response is <.
I experienced this error "SyntaxError: Unexpected token m in JSON at position", where the token 'm' can be any other characters.
It turned out that I missed one of the double quotes in the JSON object when I was using RESTconsole for DB test, as {"name: "math"}, the correct one should be {"name": "math"}
It took me a lot effort to figure out this clumsy mistake. I am afraid others would run into similar bummers.
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.
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