ts-r
  • Error
  • Reported by the lexer and parser

TS1162

An object member cannot be declared optional.

A method or property in an object literal is marked optional with `?`. Optional markers belong in types, not in object literals.

What it means

In an object literal every member exists, so ? after a member name has no meaning. Optional members are declared in the object's type (an interface or type literal).

Example

index.ts
export const o = { a?() { return 1; } };
ts-r-check -p tsconfig.json --pretty false ts-r output
index.ts(1,21): error TS1162: An object member cannot be declared optional.

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

  • Remove the ?.
  • Declare the optional member in a type and annotate the object with it: const o: { a?(): number } = {}.