clean-functions

name	clean-functions
description	Use when writing, fixing, editing, or refactoring TypeScript functions. Enforces Clean Code principles—maximum 3 arguments, single responsibility, no flag parameters.
when_to_use	Also trigger on: functions (or React components) with 4+ parameters/props, boolean flag parameters like `isTest`, functions that mutate their parameters (e.g. push to an input array), unused exports or dead helper functions, or asks like "too many props", "split this function", "is this still used".

Clean Functions

F1: Too Many Arguments (Maximum 3)

// Bad - too many parameters
function createUser(
  name: string,
  email: string,
  age: number,
  country: string,
  timezone: string,
  language: string,
  newsletter: boolean
) {
  // ...
}

// Good - use a typed object
type UserData = {
  name: string;
  email: string;
  age: number;
  country: string;
  timezone: string;
  language: string;
  newsletter: boolean;
};

function createUser(data: UserData) {
  // ...
}

More than 3 arguments means your function is doing too much or needs a data structure.

F2: No Output Arguments

Don't modify arguments as side effects. Return values instead.

type Report = {
  content: string;
};

// Bad - modifies argument
function appendFooter(report: Report): void {
  report.content += "\n---\nGenerated by System";
}

// Good - returns new value
function withFooter(report: Report): Report {
  return {
    ...report,
    content: `${report.content}\n---\nGenerated by System`,
  };
}

F3: No Flag Arguments

Boolean flags mean your function does at least two things.

// Bad - function does two different things
function render(isTest: boolean) {
  if (isTest) {
    renderTestPage();
  } else {
    renderProductionPage();
  }
}

// Good - split into two functions
function renderTestPage() {}
function renderProductionPage() {}

F4: Delete Dead Functions

If it's not called, delete it. No "just in case" code. Git preserves history.