typescript / expert
Snippet
Recursive Template Literal Type Parsing
This snippet uses template literal types and recursive conditional types to extract dynamic path parameters from a string literal at compile time. It demonstrates how TypeScript can parse strings to build complex object types based on naming conventions like ':param'.
snippet.ts
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type ExtractParams<T extends string> =T extends `${string}:${infer Param}/${infer Rest}`? { [K in Param | keyof ExtractParams<Rest>]: string }: T extends `${string}:${infer Param}`? { [K in Param]: string }: {};const route = "/user/:id/posts/:postId";type RouteParams = ExtractParams<typeof route>;// Result: { id: string; postId: string; }
Breakdown
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T extends `${string}:${infer Param}/${infer Rest}`
Checks if the string contains a colon followed by a segment before a slash, capturing both the parameter and the remainder.
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{ [K in Param | keyof ExtractParams<Rest>]: string }
Recursively maps the captured parameter and joins it with parameters extracted from the rest of the string.