---

name: typescript user-invocable: false description: This skill should be used when the user asks to "configure TypeScript", "fix type errors", "use dayjs", "add type definitions", "set up React with TypeScript", mentions ".ts" or ".tsx" files, or asks about TypeScript best practices or TypeScript-specific tooling.

TypeScript Skill

Rules

Note that these are not hard-and-fast rules. If there's a good reason not to apply a rule, don't apply it.

Alphabetical Order

Maintain alphabetical order for better readability and consistency:

• Function parameters - Order by parameter name
• Object literal fields - Sort by key name
• Type definitions - Arrange fields alphabetically
• Class properties - Order by property name

Example (type definitions):

Copy// bad
type User = {
  name: string;
  age: number;
  email: string;
};

// good
type User = {
  age: number;
  email: string;
  name: string;
};

Biome

Use BiomeJS for linting and formatting JavaScript and TypeScript code. Look for a biome.jsonc file.

Exception: project already uses ESLint and Prettier.

dayjs for date and time calculations

Use the dayjs library for date calculations. Avoid using the native JavaScript Date object.

Example:

Copyimport dayjs from "dayjs";

const now = dayjs();
const tomorrow = now.add(1, "day");

No any type

Never use the any type.

No nested ternary operators

Avoid nested ternary operators. Use if/else statements or early returns instead.

Example:

Copy// bad
const result = a ? b : c ? d : e;

// good
if (a) {
  return b;
}
if (c) {
  return d;
}
return e;

Never return a value in forEach callbacks

Example:

Copy[].forEach(() => {
  return 1; // bad
});

[].forEach(() => {
  // good
});

Another example:

Copy[].forEach((item) => console.log(item)); // bad

[].forEach((item) => {
  console.log(item); // good
});

Prefer type instead of interface

Use type instead of interface for declaring types.

Comment Dividers

Use centered comment dividers for major section breaks:

Format (80 chars total):

Copy// -------------------------------------------------------------------------- //
//                                   TITLE                                    //
// -------------------------------------------------------------------------- //

Rules:

• Total width: 80 characters
• Title: UPPERCASE, centered with spaces
• Border line: dashes - filling the space between // and //

When to use:

• Major logical sections (imports, types, constants, main logic, exports)
• Separating distinct feature areas
• NOT for every function or small grouping

Example:

Copy// -------------------------------------------------------------------------- //
//                                   IMPORTS                                  //
// -------------------------------------------------------------------------- //

import { Effect } from "effect";

// -------------------------------------------------------------------------- //
//                                    TYPES                                   //
// -------------------------------------------------------------------------- //

type Config = {
  name: string;
};