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

TS1200

Line terminator not permitted before arrow.

An arrow function has a line break between its parameters and `=>`. Keep `=>` on the same line as the closing parenthesis.

What it means

JavaScript doesn't allow a line break before =>. The parameter list and the arrow must be on the same line; the body can start on the next line.

Example

index.ts
const double = (n: number)
  => n * 2;
export {};
ts-r-check -p tsconfig.json --pretty false ts-r output
index.ts(2,3): error TS1200: Line terminator not permitted before arrow.

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

  • Move => up: const double = (n: number) => followed by the body on the next line.