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

TS8016

Type assertion expressions can only be used in TypeScript files.

A type assertion (`x as T` or `<T>x`) appears in a JavaScript file. Use a JSDoc cast or rename the file to .ts.

What it means

Type assertions 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
const input = document.querySelector("input") as HTMLInputElement;
cargo run -p ts_r_parser --example dump -- index.js --ts-in-js report ts-r output
index.js(1,50): error TS8016: Type assertion expressions 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

  • Use a JSDoc cast: /** @type {HTMLInputElement} */ (document.querySelector("input")).
  • Rename the file to .ts if it's meant to be TypeScript.