E0321: expected '?' to mark tuple element as optional
TypeScript tuple types can contain optional elements. These optional elements must be last. It is a syntax error to write a required tuple element after an optional one:
function parseVersion(
): [number, number?, string] {
/* ... */
}
To fix this error, mark the tuple element as optional by adding ?
:
function parseVersion(
): [number, number?, string?] {
/* ... */
}
Alternatively, use a union type:
function parseVersion(
): [number, number?]
| [number, string]
| [number, number, string] {
/* ... */
}
Introduced in quick-lint-js version 2.10.0.