@comscen/islib

Because typeof undefined === 'undefined' is SO much typing.

A collection of blazing-fast is* utility functions for JavaScript and TypeScript. Over 80 functions covering numbers, strings, arrays, types, dates, and booleans.

Heavily inspired by the legendary is-even package (which has 900k+ weekly downloads), but with slightly more functions. Just slightly.

Installation

npm install @comscen/islib

Usage

import {
  isEven,
  isPrime,
  isPalindrome,
  isURL,
  isLeapYear,
} from "@comscen/islib";

isEven(42); // true  (bitwise AND, obviously)
isPrime(7919); // true  (6k±1 optimized)
isPalindrome("racecar"); // true  (two-pointer, zero allocations)
isURL("https://example.com"); // true
isLeapYear(2000); // true
isHappy(7); // true  (Floyd's cycle detection)
isFibonacci(89); // true  (perfect square math trick, O(1))

API

Numbers

| Function | Description | Algorithm | | ------------------------ | ----------------------- | --------------------------------- | | isEven(n) | n is even | (n & 1) === 0 bitwise AND | | isOdd(n) | n is odd | (n & 1) !== 0 bitwise AND | | isPositive(n) | n > 0 | comparison | | isNegative(n) | n < 0 | comparison | | isZero(n) | n === 0 | strict equality | | isPowerOfTwo(n) | n is a power of 2 | (n & (n-1)) === 0 bit trick | | isInteger(n) | no fractional part | Number.isInteger | | isFloat(n) | finite non-integer | isFinite && !isInteger | | isNaN(n) | not a number | n !== n identity trick | | isInfinity(n) | ±Infinity | equality check | | isPrime(n) | prime number | 6k±1 trial division | | isPerfectSquare(n) | perfect square | Math.sqrt floor check | | isFibonacci(n) | Fibonacci number | 5n²±4 perfect square check (O(1)) | | isDivisibleBy(n, d) | n % d === 0 | modulo | | isMultipleOf(n, m) | alias for isDivisibleBy | modulo | | isWholeNumber(n) | non-negative integer | isInteger && n >= 0 | | isInRange(n, min, max) | min ≤ n ≤ max | comparison | | isBetween(n, min, max) | min < n < max | strict comparison | | isPerfectNumber(n) | sum of divisors = n | trial division | | isTriangular(n) | triangular number | 8n+1 perfect square check | | isNumericPalindrome(n) | palindrome number | two-pointer scan | | isArmstrong(n) | narcissistic number | digit power sum | | isDigitAnagram(n, m) | same digits | sorted digit comparison | | isHappy(n) | happy number | Floyd's cycle detection |

Strings

| Function | Description | | --------------------- | -------------------------------------- | | isPalindrome(s) | reads same forwards and backwards | | isAnagram(s1, s2) | same characters, different order | | isEmail(s) | valid email address | | isURL(s) | valid http/https/ftp URL | | isEmpty(s) | length === 0 | | isBlank(s) | empty or whitespace-only | | isUpperCase(s) | all uppercase letters | | isLowerCase(s) | all lowercase letters | | isAlpha(s) | only a–z, A–Z | | isAlphanumeric(s) | only a–z, A–Z, 0–9 | | isHexColor(s) | valid CSS hex color (#RGB or #RRGGBB) | | isIPv4(s) | valid IPv4 address | | isIPv6(s) | valid IPv6 address | | isJSON(s) | valid JSON string | | isNumericString(s) | coercible to a finite number | | isTitleCase(s) | Title Case formatting | | isBase64(s) | valid base64 encoding | | isUUID(s) | valid UUID v1–v5 | | isWhitespace(s) | non-empty, only whitespace chars | | isASCII(s) | only code points 0–127 | | isSemVer(s) | valid semantic version | | isStrongPassword(s) | ≥8 chars, upper, lower, digit, special | | isHexString(s) | valid hexadecimal byte string |

Arrays

| Function | Description | | ------------------------------- | ---------------------------------------- | | isArrayEmpty(arr) | arr.length === 0 | | isSorted(arr) | ascending order | | isSortedDesc(arr) | descending order | | isSubset(arr, parent) | all elements exist in parent | | isUnique(arr) | no duplicate elements | | isFlat(arr) | no nested arrays | | isEqualArray(a, b) | same elements in same order (===) | | isArrayContaining(arr, value) | value exists in array | | isAll(arr, predicate) | every element satisfies predicate | | isAny(arr, predicate) | at least one element satisfies predicate | | isNone(arr, predicate) | no element satisfies predicate |

Types

| Function | Description | | ---------------------- | -------------------------------------------- | | isArray(v) | Array.isArray | | isObject(v) | plain object (not array, not class instance) | | isFunction(v) | callable value | | isString(v) | string primitive | | isNumber(v) | number primitive (excludes NaN) | | isFiniteNumber(v) | finite number (excludes NaN and ±Infinity) | | isBoolean(v) | true or false | | isNull(v) | === null | | isUndefined(v) | === undefined | | isNullOrUndefined(v) | null or undefined | | isSymbol(v) | Symbol | | isBigInt(v) | BigInt | | isDate(v) | valid Date instance | | isRegExp(v) | RegExp | | isPromise(v) | Promise or thenable | | isIterable(v) | implements Symbol.iterator | | isMap(v) | Map instance | | isSet(v) | Set instance | | isError(v) | Error instance | | isClassInstance(v) | non-plain object with prototype |

Dates

| Function | Description | | --------------------- | -------------------------- | | isLeapYear(year) | Gregorian leap year | | isWeekend(date) | Saturday or Sunday | | isWeekday(date) | Monday through Friday | | isBefore(d1, d2) | d1 < d2 | | isAfter(d1, d2) | d1 > d2 | | isToday(date) | same calendar day as today | | isValidDate(value) | valid Date object | | isPast(date) | before now | | isFuture(date) | after now | | isSameDay(d1, d2) | same year/month/day | | isSameMonth(d1, d2) | same year/month | | isSameYear(d1, d2) | same year |

Booleans

| Function | Description | | ------------------------ | ---------------------------- | | isTrue(v) | === true | | isFalse(v) | === false | | isTruthy(v) | coerces to true | | isFalsy(v) | coerces to false | | isStrictlyTrue(v) | alias for isTrue | | isStrictlyFalse(v) | alias for isFalse | | isEitherBoolean(v) | true or false | | isAllTruthy(...values) | all values are truthy | | isAnyTruthy(...values) | at least one value is truthy |

Performance

Most functions run in O(1) time with zero heap allocations. Key optimizations:

• Bitwise tricks: isEven / isOdd use bitwise AND instead of modulo
• Power of two: isPowerOfTwo uses the classic (n & (n - 1)) === 0 single-instruction trick
• NaN detection: isNaN uses n !== n — the fastest possible NaN check (NaN is the only value not equal to itself)
• Fibonacci: isFibonacci uses the 5n²±4 perfect square theorem — O(1), no sequence generation
• Triangular numbers: isTriangular uses the 8n+1 perfect square theorem — O(1)
• Primality: isPrime uses 6k±1 trial division, checking ~√n/3 candidates
• Happy numbers: isHappy uses Floyd's two-pointer cycle detection — no growing Sets
• Anagram: isAnagram uses a Map for O(n) character frequency instead of sorting
• Subset: isSubset builds a parent Set for O(m+n) instead of O(m·n)
• Palindrome: isPalindrome / isNumericPalindrome use two-pointer scan — no string reversal allocation
• ASCII: isASCII uses a raw charCode loop — no regex engine overhead

Tree-shaking

@comscen/islib ships both CommonJS and ESM builds. Any modern bundler will tree-shake unused functions automatically.

// Only isEven ends up in your bundle
import { isEven } from "@comscen/islib";

Zero dependencies

No runtime dependencies. TypeScript types are included.

License

MIT