How to Fix SyntaxError: Unexpected end of JSON input

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How to Fix SyntaxError: Unexpected end of JSON input

Working with JSON in JavaScript and came across this dreaded message?

SyntaxError: Unexpected end of JSON input

Fortunately, our Experts are here to help you understand what this error means and, more importantly, how to fix it.

What Triggers the “Unexpected End of JSON Input” Error?

This error occurs when the JSON parser expects more data but reaches the end of the input instead. In simple terms, it’s like reading a sentence that suddenly cuts off.

You’re left hanging, and so is the parser.

This usually happens when we are trying to parse an incomplete, empty, or malformed JSON string, often returned from an API, file, or localStorage.

This issue isn’t exclusive to JavaScript. Developers working with various backend frameworks and databases, like Laravel, may also face JSON-related issues such as encoding errors.

Why This Error Occurs

Here are some of the most common causes:

• The data was only partially received or generated.
• A server responded with nothing when JSON was expected.
• The structure of the JSON is broken or truncated.
• For example, forgetting to `await` a `fetch()` result before parsing it.

It’s important to remember that this error isn’t about the code. It’s about the data being parsed. `JSON.parse()` expects a fully-formed JSON string, and if it gets an empty string or broken data, it will throw this error every time.

Malformed JSON can also lead to application-level issues if you work with structured data in databases. For instance, updating JSONB fields in PostgreSQL requires proper syntax to avoid errors and ensure data integrity.

How to Debug the Error

1. First, we can use online tools like JSONLint to check if the JSON structure is complete and correct. This helps catch syntax problems before they reach the code.
2. Furthermore, make sure the response isn’t empty before calling `JSON.parse()`:

   if (responseText) {
   
   const data = JSON.parse(responseText);
   
   }
   
   
3. To safely handle optional or potentially empty data, use default values:

   const data = JSON.parse(responseText || '{}');
4. Also, make sure the async calls are fully awaited:

   const res = await fetch('/api/data');
   
   const json = await res.text();
   
   if (json) {
   
   const data = JSON.parse(json);
   
   }
   
   
5. We can use tools like Postman, cURL, or the browser’s Developer Tools under the Network tab to see exactly what the server is sending. Right-click on the network request, open it in a new tab, and inspect the raw response.
6. Data pulled from `localStorage`, cookies, or local files might be outdated or corrupted. Always validate before parsing.

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Conclusion

The “Unexpected end of JSON input” error is a common error, especially when working with APIs or dynamic data sources. But it’s also one of the easiest errors to avoid if you have the right guide.

In brief, our Support Experts demonstrated how to fix SyntaxError: Unexpected end of JSON input.