JavaScript/TypeScript Standards

Apply these standards when writing or reviewing JavaScript/TypeScript code.

Core Coding Standards

Language Features

• Use JavaScript with ES2022 features and Node.js (22+) 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

Code Quality

• Keep the code simple, readable, 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

Syntax Preferences

• Prefer functions over classes
• Use arrow functions for callbacks
• Use const for variables that are not reassigned, and let for those that are
• Use template literals for strings that require interpolation
• Use destructuring for objects and arrays where appropriate
• Use for...of loops for iterating over arrays and for...in loops for iterating over objects
• Use semicolons at the end of statements
• Prefer single quotes for strings

Component & Module Structure

• Use function-based components
• Use arrow functions for callbacks
• Organize code by feature/module
• Write clear, concise JSDoc/TSDoc comments when necessary

Testing Standards

Framework

• Use Vitest for testing

Best Practices

• Write tests for all new features and bug fixes
• Ensure tests cover edge cases and error handling
• Name tests clearly: shouldDoSomethingWhenCondition()
• NEVER change the original code to make it easier to test; instead, write tests that cover the original code as it is

Examples

Good: Modern async/await

const fetchUserData = async userId => {
	const response = await fetch(`/api/users/${userId}`)
	const data = await response.json()
	return data
}

Bad: Promises with .then()

const fetchUserData = userId => {
	return fetch(`/api/users/${userId}`)
		.then(response => response.json())
		.then(data => data)
}

Good: Descriptive names and const

const maxRetryAttempts = 3
const isValidEmail = email => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email)

Bad: Unclear names and var

var x = 3
var check = e => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(e)

Good: Template literals and destructuring

const getUserGreeting = ({ firstName, lastName }) => {
	return `Hello, ${firstName} ${lastName}!`
}

Bad: String concatenation

const getUserGreeting = user => {
	return 'Hello, ' + user.firstName + ' ' + user.lastName + '!'
}

When to Apply

Apply these standards when:

• Creating new JavaScript/TypeScript files
• Reviewing or refactoring existing code
• User asks about JavaScript/TypeScript best practices
• Working with Node.js projects
• Writing or reviewing tests with Vitest