check-toolkit

A lightweight TypeScript utility library: type guards plus small helpers for objects, arrays, strings, cloning, and functions. Zero runtime dependencies — import only what you need.

Why check-toolkit?

• Utilities + type guards — pick / groupBy / debounce alongside isNotNil and friends
• Lightweight — focused helpers without a full lodash-sized surface
• Tree-shakeable — each function is imported separately
• Zero runtime dependencies — nothing extra in your bundle
• Typed — type guards like isNotNil and isPlainObject narrow types in TypeScript
• AI-friendly catalog — machine-readable API at check-toolkit/catalog so agents use real exports, not invented ones

Use it when you want a small ESM toolkit with solid TypeScript narrowing, not a large utility framework.

Installation

npm install check-toolkit

Usage

import { isString, isPlainObject, pick } from "check-toolkit";

console.log(isString("test")); // true
console.log(isPlainObject({ a: 1 })); // true

const payload = pick({ a: 1, b: 2, c: 3 }, ["a", "c"]);
// { a: 1, c: 3 }

Available Functions

Type Checking

• isSymbol - Check if value is a symbol
• isArray - Check if value is an array
• isArrayLike - Check if value is array-like
• isNan - Check if value is NaN
• isObject - Check if value is an object
• isNull - Check if value is null
• isFunction - Check if value is a function
• isNumber - Check if value is a number
• isString - Check if value is a string
• isBoolean - Check if value is a boolean
• isPlainObject - Check if value is a plain object
• isUndefined - Check if value is undefined
• isNotUndefined - Check if value is not undefined
• isNil - Check if value is null or undefined
• isNotNil - Check if value is not null and not undefined
• isNotNaN - Check if value is not NaN
• isEmpty - Check if value is empty
• isEqual - Check if two values are equal
• isMatch - Check if object matches source

Object Operations

• pick - Creates a new object with only the specified keys
• omit - Creates a new object without the specified keys
• pickBy - Creates a new object with entries that satisfy a predicate
• omitBy - Creates a new object without entries that satisfy a predicate

Array Operations

• compact - Removes falsy values from an array
• countBy - Counts elements grouped by iteratee result
• uniq - Creates an array with unique values
• uniqBy - Like uniq but accepts an iteratee
• groupBy - Groups array elements by iteratee result
• partition - Splits an array into two groups by predicate
• sortBy - Creates a sorted copy by iteratee result
• difference - Create an array of unique values not included in other arrays
• differenceBy - Like difference but accepts iteratee
• differenceWith - Like difference but accepts comparator
• keyBy - Creates an object composed of keys generated from array

String Operations

• capitalize - Uppercases the first character only (not title case; uses toUpperCase)
• camelCase - Converts a string to camel case
• kebabCase - Converts a string to kebab case
• snakeCase - Converts a string to snake case
• startCase - Converts each word to start case (title-style)
• escape - Escapes HTML special characters
• unescape - Unescapes HTML special characters
• escapeRegExp - Escapes RegExp special characters

Clone Operations

• clone - Creates a shallow clone of a value
• cloneDeep - Creates a deep clone of a value
• cloneWith - Creates a shallow clone with a customizer
• cloneDeepWith - Creates a deep clone with a customizer

Function Utilities

• debounce - Creates a debounced function
• throttle - Creates a throttled function
• noop - No-op default callback
• identity - Returns the first argument unchanged
• once - Invokes a function at most once

Math

• clamp - Clamps a number between min and max

Promise

• delay - Resolves after the specified milliseconds

AI / Agent integration

check-toolkit ships a vendor-neutral machine-readable catalog (not an LLM runtime). Any tool that can read JSON or docs can use it.

Catalog (source of truth)

import catalog from "check-toolkit/catalog" with { type: "json" };
// or read node_modules/check-toolkit/ai/catalog.json / ai/catalog.json from the repo

Each entry includes signature, intents, narrows, examples, and antiPatterns. The root also lists notIncluded APIs (for example get, merge, memoize) so agents do not hallucinate them.

llms.txt

A compact digest generated from the catalog:

• In the repo: ai/llms.txt
• On GitHub: https://raw.githubusercontent.com/neturuDev/check-toolkit/main/ai/llms.txt

Regenerate / validate (also runs as part of npm run build):

npm run generate:ai

Agent skill (optional)

For coding agents that support Agent Skills, see skills/check-toolkit/SKILL.md. Prefer the catalog as the API source of truth; the skill only encodes prefer/narrowing rules.

Testing

To run the test suite:

npm run test

To build the project:

npm run build

To start development server:

npm run dev

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

MIT License

Originally created by Volodymyr Cherevchuk