@eroyeroy/utils

A fully typed TypeScript utility library with tree-shakeable subpath imports and zero runtime dependencies.

Installation

npm

npm i @eroyeroy/utils

pnpm

pnpm add @eroyeroy/utils

yarn

yarn add @eroyeroy/utils

bun

bun add @eroyeroy/utils

Usage

Import from the root or from any subpath:

// Full import
import { groupBy, isEmail, formatBytes } from "@eroyeroy/utils"

// Subpath import (smallest bundle)
import { groupBy } from "@eroyeroy/utils/array"
import { isEmail } from "@eroyeroy/utils/validation"
import { formatBytes } from "@eroyeroy/utils/format"

Modules

Module	Subpath	Functions
Array	`@eroyeroy/utils/array`	34
Guards	`@eroyeroy/utils/guards`	14
String	`@eroyeroy/utils/string`	11
Object	`@eroyeroy/utils/object`	9
Number	`@eroyeroy/utils/number`	10
Async	`@eroyeroy/utils/async`	4
Function	`@eroyeroy/utils/function`	6
URL	`@eroyeroy/utils/url`	7
Format	`@eroyeroy/utils/format`	4
Date	`@eroyeroy/utils/date`	16
Validation	`@eroyeroy/utils/validation`	10

Array

import { ... } from "@eroyeroy/utils/array"

`arrayIncludes(array, value)`

Typed Array.prototype.includes. Narrows the type of value to T[number] on true.

const roles = ["admin", "user"] as const
arrayIncludes(roles, "admin") // => true, typed as "admin" | "user"

`averageBy(array, key)`

Average of a numeric key. Returns 0 for empty arrays.

averageBy([{ score: 10 }, { score: 20 }, { score: 30 }], "score") // => 20

`chunkArray(array, size)`

Splits into chunks of at most size elements.

chunkArray([1, 2, 3, 4, 5], 2) // => [[1, 2], [3, 4], [5]]

`compactArray(array)`

Removes null and undefined.

compactArray([1, null, 2, undefined, 3]) // => [1, 2, 3]

`countBy(array, key)`

Counts occurrences of each value of key.

countBy([{ role: "admin" }, { role: "user" }, { role: "admin" }], "role")
// => { admin: 2, user: 1 }

`dropArray(array, count)`

Removes the first count elements.

dropArray([1, 2, 3, 4], 2) // => [3, 4]

`findArrayItemByKey(array, key, value)`

Finds the first item where item[key] === value.

findArrayItemByKey([{ id: 1, name: "Alice" }, { id: 2, name: "Bob" }], "id", 2)
// => { id: 2, name: "Bob" }

`firstArrayItem(array)`

Returns the first element (typed as non-undefined for non-empty tuples).

firstArrayItem([1, 2, 3]) // => 1
firstArrayItem([])         // => undefined

`flattenArray(array)`

Flattens one level of nesting.

flattenArray([[1, 2], [3, 4], [5]]) // => [1, 2, 3, 4, 5]

`groupBy(array, key)`

Groups items by the value of a key.

groupBy([{ role: "admin", name: "Alice" }, { role: "user", name: "Bob" }], "role")
// => { admin: [{ role: "admin", name: "Alice" }], user: [{ role: "user", name: "Bob" }] }

`hasArrayItemByKey(array, key, value)`

Returns true if any item matches item[key] === value.

hasArrayItemByKey([{ id: 1 }, { id: 2 }], "id", 2) // => true

`insertArrayItem(array, item, index?)`

Inserts at index (defaults to end).

insertArrayItem([1, 2, 4], 3, 2) // => [1, 2, 3, 4]

`isArray(value)`

Type guard for arrays.

isArray([1, 2, 3]) // => true

`isEmptyArray(value)`

Returns true if value is an array with zero elements.

isEmptyArray([]) // => true

`isFilledArray(value)`

Returns true if value is an array with at least one element.

isFilledArray([1]) // => true

`lastArrayItem(array)`

Returns the last element (typed as non-undefined for non-empty tuples).

lastArrayItem([1, 2, 3]) // => 3

`mapArrayToRecord(array, key)`

Transforms an array to a record keyed by key.

mapArrayToRecord([{ id: 1, name: "Alice" }, { id: 2, name: "Bob" }], "id")
// => { 1: { id: 1, name: "Alice" }, 2: { id: 2, name: "Bob" } }

`maxBy(array, key)`

Returns the item with the maximum value of key.

maxBy([{ age: 25 }, { age: 30 }, { age: 20 }], "age") // => { age: 30 }

`minBy(array, key)`

Returns the item with the minimum value of key.

minBy([{ age: 25 }, { age: 30 }, { age: 20 }], "age") // => { age: 20 }

`moveArrayItem(array, fromIndex, toIndex)`

Moves an item to a new position.

moveArrayItem([1, 2, 3, 4], 0, 3) // => [2, 3, 4, 1]

`partitionArray(array, predicate)`

Splits into [matched, unmatched].

partitionArray([1, 2, 3, 4, 5], n => n % 2 === 0) // => [[2, 4], [1, 3, 5]]

`rangeArray(end)` / `rangeArray(start, end)`

Creates a range of integers.

rangeArray(5)    // => [0, 1, 2, 3, 4]
rangeArray(1, 5) // => [1, 2, 3, 4, 5]
rangeArray(5, 1) // => [5, 4, 3, 2, 1]

`removeArrayItem(array, item)`

Removes all occurrences of an item by reference.

removeArrayItem([1, 2, 3, 2], 2) // => [1, 3]

`removeArrayItemByKey(array, key, value)`

Removes all items where item[key] === value.

removeArrayItemByKey([{ id: 1 }, { id: 2 }, { id: 1 }], "id", 1)
// => [{ id: 2 }]

`replaceArrayItem(array, itemToReplace, replacement)`

Replaces all items equal by reference.

replaceArrayItem([1, 2, 3, 2], 2, 99) // => [1, 99, 3, 99]

`replaceArrayItemByKey(array, key, value, replacement)`

Replaces all items matching item[key] === value. Accepts a function.

replaceArrayItemByKey([{ id: 1, x: 0 }], "id", 1, item => ({ ...item, x: 99 }))
// => [{ id: 1, x: 99 }]

`shuffleArray(array, random?)`

Fisher-Yates shuffle. Accepts a custom RNG for deterministic results.

shuffleArray([1, 2, 3, 4, 5]) // => e.g. [3, 1, 5, 2, 4]

`sortBy(array, key, direction?)`

Sorts by key ("asc" or "desc"). Supports strings, numbers, booleans, and Dates.

sortBy([{ age: 30 }, { age: 20 }, { age: 25 }], "age")        // ascending
sortBy([{ age: 30 }, { age: 20 }, { age: 25 }], "age", "desc") // descending

`sumBy(array, key)`

Sum of a numeric key.

sumBy([{ price: 10 }, { price: 20 }, { price: 30 }], "price") // => 60

`takeArray(array, count)`

Returns the first count elements.

takeArray([1, 2, 3, 4], 2) // => [1, 2]

`toggleArrayItem(array, item)`

Removes the item if present, appends if absent. Useful for selection sets.

toggleArrayItem([1, 2, 3], 2) // => [1, 3]
toggleArrayItem([1, 3], 2)    // => [1, 3, 2]

`uniqueArray(array)`

Removes duplicate values, preserving insertion order.

uniqueArray([1, 2, 1, 3, 2]) // => [1, 2, 3]

`uniqueBy(array, key)`

Removes duplicates based on a key, keeping the first occurrence.

uniqueBy([{ id: 1, v: "a" }, { id: 1, v: "b" }, { id: 2, v: "c" }], "id")
// => [{ id: 1, v: "a" }, { id: 2, v: "c" }]

`updateArrayItemByKey(array, key, value, update)`

Updates all items matching item[key] === value. Accepts a partial object or function.

updateArrayItemByKey([{ id: 1, x: 0 }, { id: 2, x: 0 }], "id", 1, { x: 99 })
// => [{ id: 1, x: 99 }, { id: 2, x: 0 }]

updateArrayItemByKey([{ id: 1, x: 5 }], "id", 1, item => ({ ...item, x: item.x * 2 }))
// => [{ id: 1, x: 10 }]

Guards

import { ... } from "@eroyeroy/utils/guards"

Function	Description
`isString(value)`	`value is string`
`isNumber(value)`	`value is number` (excludes `NaN`)
`isBoolean(value)`	`value is boolean`
`isNull(value)`	`value is null`
`isUndefined(value)`	`value is undefined`
`isNullish(value)`	`value is null \| undefined`
`isDefined(value)`	`value is T` — useful for `array.filter(isDefined)`
`isObject(value)`	Plain object (not null, not array)
`isFunction(value)`	`value is (...args) => unknown`
`isDate(value)`	`value instanceof Date`
`isError(value)`	`value instanceof Error`
`isSymbol(value)`	`value is symbol`
`isBigInt(value)`	`value is bigint`
`isRegExp(value)`	`value instanceof RegExp`

[1, null, 2, undefined].filter(isDefined) // => [1, 2]

String

import { ... } from "@eroyeroy/utils/string"

Function	Description	Example
`capitalize(str)`	Uppercases the first character	`"hello"` → `"Hello"`
`camelCase(str)`	Converts to `camelCase`	`"hello_world"` → `"helloWorld"`
`snakeCase(str)`	Converts to `snake_case`	`"helloWorld"` → `"hello_world"`
`kebabCase(str)`	Converts to `kebab-case`	`"HelloWorld"` → `"hello-world"`
`pascalCase(str)`	Converts to `PascalCase`	`"hello-world"` → `"HelloWorld"`
`truncate(str, max, suffix?)`	Truncates to `max` chars	`truncate("Hello, World!", 8)` → `"Hello..."`
`slugify(str)`	URL-friendly slug	`"Hello, World!"` → `"hello-world"`
`reverseString(str)`	Reverses characters	`"hello"` → `"olleh"`
`maskString(str, visible?, char?)`	Masks all but last N chars	`maskString("1234567890")` → `"******7890"`
`countWords(str)`	Counts whitespace-separated words	`"hello world"` → `2`
`isEmptyString(str)`	True if empty or only whitespace	`""` / `" "` → `true`
`isFilledString(str)`	True if has non-whitespace content	`"hi"` → `true`

Object

import { ... } from "@eroyeroy/utils/object"

Function	Description
`pick(obj, keys)`	Returns a new object with only the specified keys
`omit(obj, keys)`	Returns a new object with the specified keys excluded
`objectKeys(obj)`	Typed `Object.keys`
`objectValues(obj)`	Typed `Object.values`
`objectEntries(obj)`	Typed `Object.entries`
`mapValues(obj, fn)`	Maps values, preserving keys
`filterValues(obj, predicate)`	Filters entries by value
`isEmptyObject(obj)`	True if no own enumerable keys
`isFilledObject(obj)`	True if at least one own enumerable key

pick({ a: 1, b: 2, c: 3 }, ["a", "c"])         // => { a: 1, c: 3 }
omit({ a: 1, b: 2, c: 3 }, ["b"])               // => { a: 1, c: 3 }
mapValues({ a: 1, b: 2 }, v => v * 2)           // => { a: 2, b: 4 }
filterValues({ a: 1, b: 2, c: 3 }, v => v > 1) // => { b: 2, c: 3 }

Number

import { ... } from "@eroyeroy/utils/number"

Function	Description	Example
`clamp(value, min, max)`	Clamps to `[min, max]`	`clamp(15, 0, 10)` → `10`
`inRange(value, min, max)`	Checks inclusive range	`inRange(5, 0, 10)` → `true`
`roundTo(value, precision)`	Rounds to N decimal places	`roundTo(1.2345, 2)` → `1.23`
`isInteger(value)`	True if safe integer	`isInteger(42)` → `true`
`isFloat(value)`	True if finite non-integer	`isFloat(1.5)` → `true`
`isPositive(value)`	True if `> 0`	`isPositive(1)` → `true`
`isNegative(value)`	True if `< 0`	`isNegative(-1)` → `true`
`isZero(value)`	True if `=== 0`	`isZero(0)` → `true`
`randomBetween(min, max)`	Random float in `[min, max)`	`randomBetween(1, 10)`
`percentageOf(value, total)`	Calculates percentage	`percentageOf(1, 4)` → `25`

Async

import { ... } from "@eroyeroy/utils/async"

`sleep(ms)`

Pauses for ms milliseconds.

await sleep(1000)

`retry(fn, options?)`

Retries an async function on failure with optional exponential backoff.

const data = await retry(() => fetch("/api").then(r => r.json()), {
  retries: 3,
  delay: 200,
  backoff: 2,
})

`withTimeout(promise, ms)`

Rejects with an error if the promise doesn't resolve within ms.

const result = await withTimeout(fetch("/api"), 5000)

`parallel(tasks, concurrency?)`

Runs async tasks with an optional concurrency limit. Preserves result order.

const results = await parallel([
  () => fetchUser(1),
  () => fetchUser(2),
  () => fetchUser(3),
], 2) // at most 2 concurrent requests

Function

import { ... } from "@eroyeroy/utils/function"

`debounce(fn, wait)`

Delays invocation until wait ms have passed since the last call.

const handleInput = debounce((value: string) => search(value), 300)

`throttle(fn, limit)`

Limits invocation to at most once per limit ms.

const handleScroll = throttle(() => updatePosition(), 100)

`memoize(fn)`

Caches results by serialized arguments.

const expensiveCalc = memoize((n: number) => n * n)
expensiveCalc(4) // computed
expensiveCalc(4) // cached

`once(fn)`

Calls fn only on the first invocation; returns the cached result thereafter.

const init = once(() => createConnection())
init() // creates connection
init() // returns cached connection

`noop()`

Does nothing. Useful as a default callback.

element.addEventListener("click", noop)

`identity(value)`

Returns the value unchanged. Useful as a default transform or selector.

[1, 2, 3].map(identity) // => [1, 2, 3]

URL

import { ... } from "@eroyeroy/utils/url"

Function	Description
`parseurl(/sitelet?url=https%3A%2F%2Fgithub.com%2FEroyEroy%2Furl)`	Parses to `URL` or returns `null` on failure
`buildurl(/sitelet?url=https%3A%2F%2Fgithub.com%2FEroyEroy%2Fbase%2C%2520params)`	Appends query params (skips null/undefined values)
`getQueryParam(url, param)`	Gets a single query param or `null`
`setQueryParam(url, param, value)`	Sets/replaces a query param
`removeQueryParam(url, param)`	Removes a query param
`isValidurl(/sitelet?url=https%3A%2F%2Fgithub.com%2FEroyEroy%2Furl)`	Returns `true` for valid absolute URLs
`joinurl(/sitelet?url=https%3A%2F%2Fgithub.com%2FEroyEroy%2Fbase%2C%2520path)`	Joins URL and path, normalizing slashes

buildUrl("https://api.example.com", { page: 1, q: "hello", sort: null })
// => "https://api.example.com/?page=1&q=hello"

getQueryParam("https://example.com?q=hello", "q") // => "hello"
joinUrl("https://example.com/api/", "/users")      // => "https://example.com/api/users"

Format

import { ... } from "@eroyeroy/utils/format"

`formatBytes(bytes, precision?)`

formatBytes(0)          // => "0 B"
formatBytes(1024)       // => "1.00 KB"
formatBytes(1048576, 1) // => "1.0 MB"

`formatDuration(ms)`

formatDuration(500)      // => "500ms"
formatDuration(5000)     // => "5s"
formatDuration(90000)    // => "1m 30s"
formatDuration(3660000)  // => "1h 1m"

`formatRelativeTime(date, now?)`

formatRelativeTime(new Date(Date.now() - 5 * 60 * 1000))     // => "5 minutes ago"
formatRelativeTime(new Date(Date.now() + 24 * 60 * 60 * 1000)) // => "in 1 day"

`formatPlural(count, singular, plural?)`

formatPlural(1, "item")             // => "item"
formatPlural(3, "item")             // => "items"
formatPlural(2, "person", "people") // => "people"

Date

import { ... } from "@eroyeroy/utils/date"

All functions return new Date objects and do not mutate inputs.

Function	Description
`isValidDate(value)`	Type guard — `Date` instance with a valid time
`addDays(date, days)`	Adds days (negative to subtract)
`addMonths(date, months)`	Adds months
`addYears(date, years)`	Adds years
`diffInDays(dateA, dateB)`	Whole days from A to B (negative if B < A)
`diffInMonths(dateA, dateB)`	Whole months from A to B
`startOfDay(date)`	`00:00:00.000` of the same day (local time)
`endOfDay(date)`	`23:59:59.999` of the same day (local time)
`startOfMonth(date)`	First day of the month at midnight
`endOfMonth(date)`	Last moment of the month
`isSameDay(dateA, dateB)`	True if same calendar day
`isBefore(date, referenceDate)`	True if `date < referenceDate`
`isAfter(date, referenceDate)`	True if `date > referenceDate`
`isToday(date)`	True if today
`isPast(date)`	True if in the past
`isFuture(date)`	True if in the future

addDays(new Date("2024-01-01"), 7)                   // => 2024-01-08
diffInDays(new Date("2024-01-01"), new Date("2024-01-08")) // => 7
isBefore(new Date("2024-01-01"), new Date("2024-06-01"))   // => true

Validation

import { ... } from "@eroyeroy/utils/validation"

Function	Description
`isEmail(value)`	Simple `local@domain.tld` format check
`isUuid(value)`	UUID v1–v5
`isNumericString(value)`	String that represents a valid number
`isAlpha(value)`	Only a–z / A–Z characters
`isAlphaNumeric(value)`	Only a–z, A–Z, 0–9 characters
`hasMinLength(value, min)`	String length ≥ min
`hasMaxLength(value, max)`	String length ≤ max
`isHexColor(value)`	`#rgb` or `#rrggbb` CSS hex color
`isIpv4(value)`	Valid IPv4 address
`isIpv6(value)`	Valid IPv6 address

isEmail("user@example.com")                          // => true
isUuid("550e8400-e29b-41d4-a716-446655440000")       // => true
isHexColor("#1A2B3C")                                // => true
isIpv4("192.168.1.1")                               // => true
isIpv6("2001:0db8:85a3:0000:0000:8a2e:0370:7334")  // => true

Documentation

Generate the full HTML API docs with:

pnpm docs

Output is written to ./docs/index.html.

Development

pnpm install      # install dependencies
pnpm test         # run tests
pnpm test:watch   # run tests in watch mode
pnpm lint         # lint source
pnpm lint:fix     # lint and auto-fix
pnpm format       # format with Prettier
pnpm check-types  # TypeScript type check
pnpm build        # build ESM + CJS bundles
pnpm ci           # lint + type-check + test + build

License

MIT

Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
.husky		.husky
docs		docs
src		src
.gitignore		.gitignore
.prettierrc		.prettierrc
LICENSE		LICENSE
README.md		README.md
eslint.config.js		eslint.config.js
package.json		package.json
pnpm-lock.yaml		pnpm-lock.yaml
tsconfig.json		tsconfig.json
tsdown.config.ts		tsdown.config.ts
typedoc.json		typedoc.json
vitest.config.ts		vitest.config.ts

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@eroyeroy/utils

Installation

Usage

Modules

Array

arrayIncludes(array, value)

averageBy(array, key)

chunkArray(array, size)

compactArray(array)

countBy(array, key)

dropArray(array, count)

findArrayItemByKey(array, key, value)

firstArrayItem(array)

flattenArray(array)

groupBy(array, key)

hasArrayItemByKey(array, key, value)

insertArrayItem(array, item, index?)

isArray(value)

isEmptyArray(value)

isFilledArray(value)

lastArrayItem(array)

mapArrayToRecord(array, key)

maxBy(array, key)

minBy(array, key)

moveArrayItem(array, fromIndex, toIndex)

partitionArray(array, predicate)

rangeArray(end) / rangeArray(start, end)

removeArrayItem(array, item)

removeArrayItemByKey(array, key, value)

replaceArrayItem(array, itemToReplace, replacement)

replaceArrayItemByKey(array, key, value, replacement)

shuffleArray(array, random?)

sortBy(array, key, direction?)

sumBy(array, key)

takeArray(array, count)

toggleArrayItem(array, item)

uniqueArray(array)

uniqueBy(array, key)

updateArrayItemByKey(array, key, value, update)