How do I fix 'Unexpected end of JSON input' in JavaScript?

Updated October 2026 · How we answer

Find where the empty string comes from

JSON.parse expects a complete JSON document. If the input is an empty string, an undefined value turned into text, or a response that was cut off, parsing fails with this message. The fastest fix is to log the raw value right before the parse call so you can see exactly what arrived.

Common sources include a fetch call that returned an error page, a file that was saved empty, or a server that closed the connection early. Check the status code and content type before you parse the body. An HTML error page is not JSON, even when you expected data.

• Log the raw value before calling JSON.parse
• Check response status codes first
• Confirm the content type is application/json
• Guard against empty strings with a simple check

Handle bad input safely

Wrap the parse in a try block so the app can show a helpful message instead of crashing. Return a fallback value or ask the user to retry. This keeps one bad response from breaking the whole page.

If the JSON comes from a file, make sure the write finished before another process reads it. Partial writes are a common reason a file looks fine in your editor but fails in code.

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