Potential Causes of the Error
- Returning Non-Object Values: One of the most common causes of the "Error: getStaticPaths must return an object" in Next.js is the failure to actually return an object. Instead, it might inadvertently return a string, array, or even `undefined`. This occurs when the developer does not properly structure the return value to comply with the expected object format.
- Missing Required Keys: Even if an object is returned, it might not contain the necessary keys Next.js expects, such as `paths` and `fallback`. Both are required for `getStaticPaths` to function properly. Failing to include these keys may lead to the error.
- Asynchronous Function without Await: When the `getStaticPaths` function involves asynchronous operations, not using `await` can result in the function returning a pending Promise instead of the required object. If the function is defined as async, any omitted `await` can lead to incorrect return value.
- Incorrect Promise Handling: Similar to issues with `await`, failing to handle Promises correctly can also cause problems. Ensuring that `Promise.all` or similar patterns are used correctly to structure the resolved values into the required object format is crucial.
- Logic Errors within the Function: Sometimes, the logic within the `getStaticPaths` function itself is flawed, resulting in early return or pathways that do not lead to returning the required object. This could be due to undefined variables or conditions that are not met.
- Misconfigured Third-party Libraries: If `getStaticPaths` relies on third-party API calls or libraries, any misconfiguration that causes these functions to fail silently or to return unexpected data structures can also lead to an improper final return from the function.
- Undefined Environment Variables: If `getStaticPaths` depends on environment variables to construct its return object (for example, for API endpoints or feature toggles) and these are not set, it may lead to undefined results and accidental return of incomplete or incorrect data structures.
// Incorrect return value example
export async function getStaticPaths() {
const res = await fetch('https://api.example.com/data');
const data = await res.json();
// Wrong: returning array instead of object
return data.paths;
}
// Correcting the error
export async function getStaticPaths() {
const res = await fetch('https://api.example.com/data');
const data = await res.json();
// Ensuring to return an object with required keys: paths, fallback
return {
paths: data.paths,
fallback: false, // or true / 'blocking', depending on needs
};
}
