EC
TS1337
TypeScriptERRORNotableSyntaxHIGH confidence

An index signature parameter type cannot be a literal type or generic type. C...

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1337): An index signature parameter type cannot be a literal type or generic type. Consider using a mapped object type instead.. This diagnostic is emitted by the TypeScript compiler when an index signature parameter type cannot be a literal type or generic type. Consider using a mapped object type instead..

Why it happens
  1. 1Incorrect number or type of generic type arguments
How to reproduce

TypeScript compiler reports TS1337 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1337
// An index signature parameter type cannot be a literal type or generic type. Consider using a mapped object type instead.

expected output

error TS1337: An index signature parameter type cannot be a literal type or generic type. Consider using a mapped object type instead.

Fix

Address the TypeScript diagnostic

WHEN When this error is reported by the compiler

Address the TypeScript diagnostic
// Run the TypeScript compiler for details:
npx tsc --noEmit
// Use the TypeScript playground to test your code:
// https://www.typescriptlang.org/play

Why this works

Review the full error message and location; the TypeScript handbook provides guidance on each error category.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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