Type Check Methods

These are utility methods for type checking.

Available Functions

Basic Type Checks

isString(value)

Checks if value is classified as a String primitive or object.

import { isString } from 'xfunc'

isString('abc')
// => true

isString(123)
// => false

isNumber(value)

Checks if value is classified as a Number primitive or object.

import { isNumber } from 'xfunc'

isNumber(123)
// => true

isNumber('123')
// => false

isBoolean(value)

Checks if value is classified as a boolean primitive or object.

import { isBoolean } from 'xfunc'

isBoolean(true)
// => true

isBoolean('true')
// => false

Null/Undefined Checks

isNil(value)

Checks if value is null or undefined.

import { isNil } from 'xfunc'

isNil(null)
// => true

isNil(undefined)
// => true

isNil(0)
// => false

isEmpty(value)

Checks if value is an empty object, collection, map, or set.

import { isEmpty } from 'xfunc'

isEmpty([])
// => true

isEmpty({})
// => true

isEmpty('')
// => true

isEmpty([1, 2, 3])
// => false

Object Type Checks

isObject(value)

Checks if value is the language type of Object.

import { isObject } from 'xfunc'

isObject({})
// => true

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

isObject(null)
// => false

isPlainObject(value)

Checks if value is a plain object.

import { isPlainObject } from 'xfunc'

isPlainObject({})
// => true

isPlainObject(new Object())
// => true

isPlainObject([1, 2, 3])
// => false

Function Checks

isFunction(value)

Checks if value is classified as a Function object.

import { isFunction } from 'xfunc'

isFunction(() => {})
// => true

isFunction(function() {})
// => true

isFunction('function')
// => false

Date and RegExp Checks

isDate(value)

Checks if value is classified as a Date object.

import { isDate } from 'xfunc'

isDate(new Date())
// => true

isDate('2023-01-01')
// => false

isRegExp(value)

Checks if value is classified as a RegExp object.

import { isRegExp } from 'xfunc'

isRegExp(/abc/)
// => true

isRegExp(new RegExp('abc'))
// => true

isRegExp('abc')
// => false

Advanced Checks

isPromise(value)

Checks if value is a Promise.

import { isPromise } from 'xfunc'

isPromise(Promise.resolve())
// => true

isPromise({ then: () => {} })
// => true

isPromise({})
// => false

isError(value)

Checks if value is an Error object.

import { isError } from 'xfunc'

isError(new Error())
// => true

isError(new TypeError())
// => true

isError({ message: 'error' })
// => false

Iterable Checks

isArrayLike(value)

Checks if value is an array-like object.

import { isArrayLike } from 'xfunc'

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

isArrayLike('hello')
// => true

isArrayLike({ length: 2, 0: 'a', 1: 'b' })
// => true

isLength(value)

Checks if value is a valid array-like length.

import { isLength } from 'xfunc'

isLength(3)
// => true

isLength(Number.MAX_SAFE_INTEGER)
// => true

isLength(-1)
// => false

isLength(3.2)
// => false

isObjectLike(value)

Checks if value is object-like (not null, typeof is 'object').

import { isObjectLike } from 'xfunc'

isObjectLike({})
// => true

isObjectLike([])
// => true

isObjectLike(() => {})
// => false

isObjectLike(null)
// => false

isPrimitive(value)

Checks if value is a primitive type.

import { isPrimitive } from 'xfunc'

isPrimitive('hello')
// => true

isPrimitive(42)
// => true

isPrimitive(null)
// => true

isPrimitive({})
// => false

isIterable(value)

Checks if value is iterable.

import { isIterable } from 'xfunc'

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

isIterable('hello')
// => true

isIterable(new Set())
// => true

isIterable({})
// => false

Utility Functions

isTypeString(value, type)

Checks if value's raw type matches the given type string.

import { isTypeString } from 'xfunc'

isTypeString('hello', 'String')
// => true

isTypeString(42, 'Number')
// => true

isTypeString(null, 'Null')
// => true

isTypeString('hello', 'Number')
// => false

toRawType(value)

Gets the raw type string of a value.

import { toRawType } from 'xfunc'

toRawType('hello')
// => 'string'

toRawType(42)
// => 'number'

toRawType(null)
// => 'null'

toRawType(undefined)
// => 'undefined'

toRawType([])
// => 'array'

makeMap(list)

Creates a mapping function to check if a value is in the given list.

import { makeMap } from 'xfunc'

const isReservedWord = makeMap(['if', 'else', 'for', 'while'])

isReservedWord('if')
// => true

isReservedWord('hello')
// => false

isNumericKey(value)

Checks if value is a numeric key.

import { isNumericKey } from 'xfunc'

isNumericKey('0')
// => true

isNumericKey('42')
// => true

isNumericKey('abc')
// => false

isNumericKey(0)
// => true

Complete List

All available type checking functions:

• isArrayLike
• isBoolean
• isDate
• isEmpty
• isError
• isFunction
• isIterable
• isLength
• isNil
• isNumber
• isObject
• isObjectLike
• isPlainObject
• isPrimitive
• isPromise
• isRegExp
• isString
• isTypeString
• toRawType
• makeMap
• isNumericKey

Each function returns a boolean value indicating whether the value matches the expected type.