Fix - unexpected end of JSON input in Node.js

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If you have ever found yourself working with APIs that return JSON data then you may have come across the error “Unexpected end of json input in Node.js“. While at first glance this error code might seem hard to tackle, in reality, its resolution can be made faster if you know what you should be looking for.

So, what is an “unexpected end of JSON input in Node.js” error code?

This type of error code will usually appear when you try to parse JSON data but have accidentally provided data that is either invalid or incomplete JSON. Put even more simply this error code will appear because the response is either interrupted, corrupted, or cut off.

Some of the common reasons you might get this error code and possible solutions include:

Network Issues

While for most people it will not have been an error code that has caused this issue, this is by far the easiest reason to fix on this list. If your network connection is unstable then you might not be able to complete the data retrieval and thus, will get this error. To avoid this all you will need to do is stabilize your network connection and ensure that no interruptions occur during data fetching.

Issues with the API

An issue with the API response is once again not something you can do a lot of things about. However, one thing you can do when using an external API is to check all of the documentation for any changes or reported issues in the response format that could have caused these issues.

Check your Raw Data for issues

Whether you have already attempted to parse your data and have gotten an error code or you want to check before parsing, it can be a good idea to print or log the raw data and inspect the content and structure before you start parsing. If you notice that there are any mistakes including characters that should not be there you can fix those ahead of time.

Catch Parsing Errors

If you can’t determine what the error is regarding on your own then you could implement an error handling around the JSON parsing process. This will keep your application running and will allow you to potentially employ a try-catch block to catch the errors and handle them.

try {
    const jsonData = JSON.parse(jsonString);
    // Use jsonData
} catch (error) {
    console.error('Error parsing JSON:', error);
    // Handle the error appropriately
}

Update all dependencies

When working with modules and libraries the main thing you can do is actually check that you are using all of the latest versions. This is because it is possible that an issue or bug in an older version might be causing the error to appear on your end, but with the update that error will have been resolved.

Data Decompression

If you are using the response in a compressed format, such as gzip, and are getting an error then you should attempt to decompress the response before parsing. Always check that you are using the correct decompression method for the libraries and environments that you are using.

JSON Online validation

There are many online tools available that could check whether you have any formatting issues or syntax errors. These online JSON validators could be the key to addressing the issues in the data and can speed up the process of actually determining what the problem is.

Some of the online website that helps in validating your JSON data

JSONLint

JSON Validator (from JSON Formatter & Validator Online)

Online JSON Viewer & Validator

Content-type header issues

Only in the case where you are using an HTTP endpoint to fetch the JSON data, the error could be the result of incorrect headers. In such cases also check the content-type header and make sure that they are set to application/json.

Assume you have a Node.js server that expects JSON data in the request body, but the client sends the data without setting the appropriate “Content-Type” header:

Server-side:

const jsonData = JSON.parse(data);
                console.log(jsonData);
                res.writeHead(200, { 'Content-Type': 'application/json' });
                res.end(JSON.stringify({ message: 'Data received successfully' }));

Client-Side:

const data = {
    name: 'John Doe',
    age: 30
};

axios.post('http://localhost:3000/data', data)
    .then(response => {
        console.log(response.data);
    })

In this case, You will be seeing the “unexpected end of JSON input” exception, Because the server expects JSON data in the request body but the client sends data without “Content-Type” header as “application/json”

This can be easily avoided by checking the “Content-Type” header and responding with an appropriate error message if it’s missing or incorrect, as shown in the server-side code above.

Conclusion

The “Unexpected end of json input in Node.js” can be caused by a variety of different issues depending on your connection, APIs, libraries, and even HTTP endpoint. As such, it is up to you to determine which issue is causing the problem. However, it can still act as a great opportunity for you to add more robust error-handling mechanisms to avoid such issues in the future.

Happy Learning!!

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Jerry Richard

Cloud Premier Engineer at Cloudera

Jerry grew up in a small town where he enjoyed playing video games. Once out of the nest, he pursued a Bachelor's degree in Computer Engineering. After college, he ultimately landed in the IT industry. Currently, he has over 10 years of experience. In his spare time, Jerry enjoys spending time with his family.

He is creator of this website - unexpectedendoffile.com, A website dedicated to share the mistake and experience learned.