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

TS8006

'{0}' declarations can only be used in TypeScript files.

An `interface`, `enum`, `namespace` or `module` declaration appears in a JavaScript file. Move it to a .ts file.

What it means

TypeScript-only declarations (interfaces, enums, namespaces, module declarations) can't appear in a .js file. The message names the kind of declaration.

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
enum Color { Red, Green }
cargo run -p ts_r_parser --example dump -- index.js --ts-in-js report ts-r output
index.js(1,6): error TS8006: 'enum' declarations 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

  • Move the declaration to a .ts or .d.ts file and import it.
  • Replace an enum with a frozen object: const Color = Object.freeze({ Red: 0, Green: 1 });.
  • Describe interfaces with JSDoc @typedef.