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

TS8008

Type aliases can only be used in TypeScript files.

A `type` alias appears in a JavaScript file. Use a JSDoc `@typedef` or move it to a .ts file.

What it means

type Name = ... declarations are TypeScript syntax and can't appear in a .js file.

ts-r's parser reports this code when it reads .js files with tsc's rules for TypeScript syntax in JavaScript. ts-r-check doesn't report it yet: today it parses .js files with the plain JavaScript grammar and reports a syntax error at the same place instead.

Example

index.js
type Id = string;
cargo run -p ts_r_parser --example dump -- index.js --ts-in-js report ts-r output
index.js(1,6): error TS8008: Type aliases can only be used in TypeScript files.

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

  • Write it as JSDoc: /** @typedef {string} Id */.
  • Move it to a .ts or .d.ts file.