TypeScript const Type Parameters: Immutable Inference and When It Beats as const
This article was written with the assistance of AI, under human supervision and review.
Most TypeScript type widening problems in generic functions stem from a single overlooked feature: const type parameters. Teams write elaborate type helpers and sprinkle as const assertions everywhere when the compiler already offers a direct solution. The gap between what developers think they need and what the language provides is a ten-line diff.
The problem manifests when you pass a literal object to a generic function. TypeScript widens { method: "GET" } to { method: string }, losing the exact literal type that downstream code depends on. The workaround—forcing callers to add as const at every call site—shifts the burden to the wrong place and creates inconsistent adoption across a codebase.
Type widening problem in generic functions
