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Requires that a workspace package may only contain TypeScript files and no JavaScript or JSX files.
Table of Contents

Conformance is available on Enterprise plans

TypeScript is a superset of JavaScript that adds optional static typing. Using TypeScript in your codebase provides the following benefits:

  • Type Safety: TypeScript is a strongly-typed language, which means that it allows you to catch errors at compile-time rather than at runtime. This can help you catch bugs earlier in the development process, making your code more reliable and easier to maintain over time.
  • Tooling: TypeScript has excellent tooling support, including autocompletion, type checking, and refactoring tools. This can help you write code faster and with fewer errors.
  • JavaScript Compatibility: TypeScript is a superset of JavaScript, which means that any valid JavaScript code is also valid TypeScript code. This means that you can gradually introduce TypeScript into your project without having to rewrite your entire codebase.
  • Scalability: TypeScript is designed to work well with large-scale applications. With features like interfaces and classes, it allows you to write code that is easier to read and maintain, even as your project grows in complexity.
Conformance errors found!
A Conformance error occurred in test "TYPESCRIPT_ONLY".
JavaScript files are not allowed. Please convert the file to TypeScript.
To find out more information and how to fix this error, visit
If this violation should be ignored, add the following entry to
and get approval from the appropriate person.
  "testName": "TYPESCRIPT_ONLY",
  "reason": "TODO: Add reason why this violation is allowed to be ignored.",
  "location": {
    "filePath": "apps/docs/src/add-numbers.js"

To fix this error, you must convert the JavaScript file to TypeScript. You can do this by changing the file extension from .js to .ts or .jsx to .tsx and adding the appropriate type annotations.

--- a/apps/docs/src/add-numbers.js
+++ b/apps/docs/src/add-numbers.ts
-export function addNumbers(a, b) {
+export function addNumbers(a: number, b: number): number {
  return a + b;

The check supports custom file globs and ignore file globs that can be specified on conformance.config.jsonc. The globs take effect from the root of the workspace package.

  "rules": {
      "files": ["**/*.js", "**/*.jsx"],
      "ignoreFiles": ["**/*.custom-config.js"]

The default configuration is:

  "rules": {
      "files": ["**/*.{cjs,mjs,js,jsx}"],
      "ignoreFiles": [
        ".next/**", // Next.js output
        ".eslintrc.{cjs,js}", // Common ESLint config file name
        "*.config.{cjs,mjs,js}", // Common config file name
        "*.setup.{cjs,mjs,js}", // Common setup file name
Last updated on June 22, 2024