Why Does `response.json()` Throw \'Unexpected End of Input\' in Fetch\'s `no-cors` Mode?

Unexpected End of Input Error When Handling CORS Response

When handling the response from a REST-API fetch call with the no-cors mode, developers may encounter a "SyntaxError: Unexpected end of input" error. This error occurs at the response.json() line and prevents the response from being parsed as JSON.

Cause

The no-cors mode restricts the availability of the response data to the browser. In this mode, the response becomes opaque, meaning that frontend JavaScript cannot access its body or headers. This limitation is designed to prevent cross-origin data access and potential security vulnerabilities.

Solution

To resolve this error, the no-cors mode must be removed from the request. This mode should not be used as a workaround for CORS issues. Instead, the following solutions should be considered:

• Configure the server to send the Access-Control-Allow-Origin response header and handle OPTIONS requests.
• Use a CORS proxy to forward the request to the server and handle the CORS headers.

Additional Information

• The documentation for the Request object explains the effects of using no-cors mode: https://developer.mozilla.org/en-US/docs/Web/API/Request/mode
• For guidance on handling CORS issues, refer to the answer at: https://stackoverflow.com/questions/23619190/no-access-control-allow-origin-header-is-present-on-the-requested-resource-whe

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