Understanding the Unexpected token Error in React and Node.js

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What Does the Error Mean?

The Unexpected token error typically arises when your code encounters an unexpected character in a JavaScript file. When dealing with JSON data, this often means that the parser found a character it didn't expect at a specific position in the JSON data string.

In simpler terms, this error typically tells you that:

You're trying to parse something as JSON that isn't valid JSON.

There is a syntax error where the code expects a certain structure but finds something else.

Common Causes

Invalid JSON Format

One of the most common causes of this error is trying to parse an invalid JSON string. Ensure that the JSON data you're working with is properly formatted. For example, a JSON object should be enclosed in curly braces {}.

Example:

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Response Not in JSON Format

When using axios or similar HTTP client libraries to fetch data from an API, ensure the response is actually JSON or correctly formatted. Sometimes, you might be trying to parse a response that is plain text or HTML.

Example:

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To fix this, ensure that the server returns a JSON response and that axios is correctly set to handle it.

Improperly Stringified JSON

Ensure that any JSON you’re working with is properly stringified and contains valid key-value pairs.

Example:

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Corrupted Data

Data may sometimes get corrupted while being retrieved or sent. Make sure data is intact and hasn’t been altered.

Server-Side Errors

Example:

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How to Troubleshoot

Check the Format: Validate JSON data using online validators or tools to ensure it is in the correct format.

Error Handling: Wrap your JSON parsing logic in try-catch blocks to capture and handle errors gracefully.

Network Inspection: Use tools like Postman or curl and browser developer tools to inspect the data being sent and received.

Logging: Log the data before parsing it to see exactly what is being worked with.

Example:

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Conclusion