tswhy‽

A community effort to enrich TypeScript diagnostics.

Editing TS1019:

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TS1019

An index signature parameter cannot have a question mark.

Unlike regular function parameters, index signature parameters cannot be marked optional. The parameter will always exist when determining the type:

interface A {
  [index?: string]: boolean;
}

Fix: Remove the question mark token.

To fix the error, just remove the ? token:

interface A {
  [index: string]: boolean;
}

syntax-error