A Next.js 15 Dynamic Route Helper Type

The types to use

export type InferGSPRTWorkup<T> =
  T extends Promise<readonly (infer U)[] | (infer U)[]> ? U : T;


export type InferGSPRT<T extends (...args: any) => any> = {
  params: Promise<InferGSPRTWorkup<ReturnType<T>>>;
};

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InferGSPRTWorkup<T>

export type InferGSPRTWorkup<T> =
  T extends Promise<readonly (infer U)[] | (infer U)[]> ? U : T;

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InferGSPRT<T>

export type InferGSPRT<T extends (...args: any) => any> = {
  params: Promise<InferGSPRTWorkup<ReturnType<T>>>;
};

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Usage

export default async function Example({ params }: InferGSPRT<typeof generateStaticParams>) {
   const { slug } = await params;
   // rest...
};

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Summary

Copy-paste the two types defined initially into a file in your code base. Use InferGSPRT within the page file of dynamic routes to infer the params object returned by generateStaticParams effortlessly.

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Nextjs versions 13 & 14

Remove the outer Promise in the InferGSPRT type definition. The params object is synchronously resolved by the exported default function prior to version 15.