Add Node.js and JavaScript code generation guidelines with Vitest testing instructions (#84)

instructions/nodejs-javascript-vitest.instructions.md

@@ -0,0 +1,30 @@
+---
+description: "Guidelines for writing Node.js and JavaScript code with Vitest testing"
+applyTo: '**/*.js, **/*.mjs, **/*.cjs'
+---
+
+# Code Generation Guidelines
+
+## Coding standards
+- Use JavaScript with ES2022 features and Node.js (20+) ESM modules
+- Use Node.js built-in modules and avoid external dependencies where possible
+- Ask the user if you require any additional dependencies before adding them
+- Always use async/await for asynchronous code, and use 'node:util' promisify function to avoid callbacks
+- Keep the code simple and maintainable
+- Use descriptive variable and function names
+- Do not add comments unless absolutely necessary, the code should be self-explanatory
+- Never use `null`, always use `undefined` for optional values
+- Prefer functions over classes
+
+## Testing
+- Use Vitest for testing
+- Write tests for all new features and bug fixes
+- Ensure tests cover edge cases and error handling
+- NEVER change the original code to make it easier to test, instead, write tests that cover the original code as it is
+
+## Documentation
+- When adding new features or making significant changes, update the README.md file where necessary
+
+## User interactions
+- Ask questions if you are unsure about the implementation details, design choices, or need clarification on the requirements
+- Always answer in the same language as the question, but use english for the generated content like code, comments or docs