ts-r
  • Error
  • Reported by the type checker

TS7015

Element implicitly has an 'any' type because index expression is not of type 'number'.

An array is indexed with a value that isn't a number, so the element type is `any`. Index with a number, or use an object or Map.

What it means

Under noImplicitAny, indexing an array or tuple with a key that isn't of type number (for example a string) can't find an element type, so the result would be an implicit any.

Example

index.ts
const names = ["a", "b"];
declare const key: string;
export const n = names[key];
ts-r-check -p tsconfig.json --pretty false ts-r output
index.ts(3,24): error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'.

Recorded by node scripts/verify-examples.mjs with ts-r built from commit 6deaf01. The example uses the default tsconfig: strict, target: es2022, module: esnext, moduleResolution: bundler.

How to fix

  • Convert the key: names[Number(key)].
  • If you meant a lookup by name, use an object type with an index signature or a Map.