nextjs - 💡(How to fix) Fix [Turbopack] TypeScript Namespace Merging causes ReferenceError during runtime [1 comments, 2 participants]

a is not defined at <unknown> (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr[root-of-the-server]__e206981a..js:23:14) at module evaluation (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr[root-of-the-server]__e206981a..js:24:3) at module evaluation (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr[root-of-the-server]e206981a..js:44:138) at module evaluation (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr[root-of-the-server]__e206981a..js:59:47) at Array.TURBOPACK__page$23$5 (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr\1e749_next_dist_185248fe..js:2670:62) at async doRender (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr\1e749_next_dist_185248fe..js:3065:28) at async handleResponse (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr\1e749_next_dist_185248fe..js:3271:32) at async Module.handler (file://C:\Playground\turbopack_issue\client.next\dev\server\chunks\ssr\1e749_next_dist_185248fe..js:3642:20)

Next.js version: 16.1.6 (Turbopack)

TL;DR

The issue can be resolved by ensuring that namespace variables are accessed correctly, likely by using the fully qualified namespace path.

Guidance

• The error message "a is not defined" suggests that the variable a is not in scope when trying to access it in the namespace Test.
• The provided minimal reproduction code shows that the issue occurs when trying to access a directly in the same namespace, but works when accessing it via the fully qualified namespace path Test.a.
• To fix the issue, update the code to use the fully qualified namespace path when accessing variables within the same namespace.
• Verify that the fix works by running next dev and checking that the error no longer occurs.

Example

export namespace Test {
    export const a = 1;
}

export namespace Test {
    export const b = Test.a + 1; // Use fully qualified namespace path
}

Notes

• The issue seems to be related to how Turbopack handles namespace variables in the provided Next.js version.
• The fix may not be necessary in other environments or versions of Next.js.

Recommendation

Apply workaround: Update the code to use fully qualified namespace paths when accessing variables within the same namespace, as shown in the example above. This should resolve the issue without requiring any version upgrades or configuration changes.