ts-r
  • Error
  • Reported by the type checker

TS2538

Type '{0}' cannot be used as an index type.

A value whose type can't be a property key is used inside [ ] as an index. Use a string, number or symbol key.

What it means

Element access obj[key] and indexed access types T[K] need a key type that can name a property. Using an object type, a boolean or similar as the index is reported.

Example

index.ts
const prices: Record<string, number> = {};
const item = { id: "a" };
export const p = prices[item];
ts-r-check -p tsconfig.json --pretty false ts-r output
index.ts(3,25): error TS2538: Type '{ id: string; }' cannot be used as an index type.

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

  • Index with a string, number or symbol: prices[item.id].
  • Use a Map if you want objects as keys.