is

defined

Signature

is.defined (value)

Description

Check if a value is defined (not null or undefined).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is not null and not undefined

Examples

is.defined(0)         // true
is.defined('')        // true
is.defined(null)      // false
is.defined(undefined) // false

nil

Signature

is.nil (value)

Description

Check if a value is null or undefined.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is null or undefined

Examples

is.nil(null)      // true
is.nil(undefined) // true
is.nil(0)         // false
is.nil('')        // false

plainObject

Signature

is.plainObject (value)

Description

Check if a value is a plain object literal (not an array, not null, not a class instance).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a plain object literal

Examples

is.plainObject({})                // true
is.plainObject({ name: 'Alice' }) // true
is.plainObject([])                // false
is.plainObject(null)              // false
is.plainObject(new Date())        // false

emptyObject

Signature

is.emptyObject (value)

Description

Check if a value is a plain object with no keys.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a plain object with no keys

Examples

is.emptyObject({})                // true
is.emptyObject({ name: 'Alice' }) // false
is.emptyObject([])                // false

nonEmptyObject

Signature

is.nonEmptyObject (value)

Description

Check if a value is a plain object with at least one key.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a plain object with at least one key

Examples

is.nonEmptyObject({ name: 'Alice' }) // true
is.nonEmptyObject({})                // false
is.nonEmptyObject([])                // false

boolean

Signature

is.boolean(value)

Description

Check if a value is a boolean.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a boolean

Examples

is.boolean(true)   // true
is.boolean(false)  // true
is.boolean(1)      // false
is.boolean('true') // false

string

Signature

is.string (value)

Description

Check if a value is a string.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a string

Examples

is.string('hello') // true
is.string('')      // true
is.string(123)     // false

emptyString

Signature

is.emptyString (value)

Description

Check if a value is a string containing only whitespace.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a string with only whitespace

Examples

is.emptyString('')      // true
is.emptyString('   ')   // true
is.emptyString('hello') // false
is.emptyString(null)    // false

nonEmptyString

Signature

is.nonEmptyString (value)

Description

Check if a value is a string containing at least one non-whitespace character.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a string with at least one non-whitespace character

Examples

is.nonEmptyString('hello') // true
is.nonEmptyString('')      // false
is.nonEmptyString('   ')   // false
is.nonEmptyString(null)    // false

regularExpression

Signature

is.regularExpression (value)

Description

Check if a value is a regular expression (instance of RegExp).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a RegExp instance

Examples

is.regularExpression(/abc/)             // true
is.regularExpression(new RegExp('abc')) // true
is.regularExpression('abc')             // false
is.regularExpression(null)              // false

hex

Signature

is.hex (value)

Description

Check if a value is a valid hexadecimal string (even length, only characters 0-9 and a-f/A-F).

Parameters

Name	Type	Required	Description
value	string	yes	The value to check

Returns

Type	Description
boolean	True if the value is a non-empty string of even length containing only hex characters

Examples

is.hex('deadbeef') // true
is.hex('DEADBEEF') // true
is.hex('ff')       // true
is.hex('abc')      // false — odd length
is.hex('0xff')     // false — 0x prefix not allowed
is.hex('')         // false — must be a non-empty string
is.hex(null)       // false — value must be a string

dataUri

Signature

is.dataUri value)

Description

Returns true if value is a valid base64 data URI, i.e. a string starting with data: and containing ;base64,.

Parameters

Name	Type	Required	Description
value	*	yes	The value to test

Returns

Type	Description
boolean	true if value is a valid base64 data URI, false otherwise

Examples

is.dataUri('data:image/png;base64,iVBORw0KGgo=') // true
is.dataUri('data:text/plain;base64,aGVsbG8=')    // true
is.dataUri('data:text/plain,hello')               // false
is.dataUri('https://example.com/image.png')       // false
is.dataUri('')                                    // false
is.dataUri(null)                                  // false

url

Signature

is.url (value, baseUrl)

Description

Check if a value is a valid URL. Optionally accepts a base URL to resolve relative URLs against.

Parameters

Name	Type	Required	Description
value	string	yes	The value to check
baseUrl	string	no	Optional base URL for resolving relative URLs

Returns

Type	Description
boolean	True if the value is a valid URL

Examples

is.url('https://example.com')              // true
is.url('https://example.com/foo?bar=1')    // true
is.url('/foo/bar', 'https://example.com')  // true
is.url('example.com')                      // false — missing protocol
is.url('/foo/bar')                         // false — relative URL without base
is.url(null)                               // false — value must be a string

email

Signature

is.email(value)

Description

Check if a value is a valid email address.

Parameters

Name	Type	Required	Description
value	string	yes	The value to check

Returns

Type	Description
boolean	True if the value is a valid email address

Examples

is.email('user@example.com')       // true
is.email('first.last@example.com') // true
is.email('user+tag@example.com')   // true
is.email('userexample.com')        // false — missing @
is.email('user@')                  // false — missing domain
is.email('@example.com')           // false — missing local part
is.email(null)                     // false — must be a string

number

Signature

number(value)

Description

Check if a value is a valid finite number (not NaN, not Infinity).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a finite number

Examples

is.number(42)       // true
is.number(3.14)     // true
is.number(NaN)      // false
is.number(Infinity) // false
is.number('42')     // false

positive

Signature

is.positive (value)

Description

Check if a value is a positive number (strictly greater than 0).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a number greater than 0

Examples

is.positive(5)   // true
is.positive(0.1) // true
is.positive(0)   // false
is.positive(-5)  // false

nonPositive

Signature

is.nonPositive (value)

Description

Check if a value is a number less than or equal to 0.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a number ≤ 0

Examples

is.nonPositive(0)  // true
is.nonPositive(-5) // true
is.nonPositive(1)  // false

negative

Signature

is.negative (value)

Description

Check if a value is a negative number (strictly less than 0).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a number less than 0

Examples

is.negative(-5)   // true
is.negative(-0.1) // true
is.negative(0)    // false
is.negative(5)    // false

nonNegative

Signature

is.nonNegative (value)

Description

Check if a value is a number greater than or equal to 0.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a number ≥ 0

Examples

is.nonNegative(0)  // true
is.nonNegative(5)  // true
is.nonNegative(-1) // false

inRange

Signature

is.inRange (value, min, max)

Description

Check if a value is within a numeric range (inclusive on both ends).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
min	number	yes	Minimum value (inclusive)
max	number	yes	Maximum value (inclusive)

Returns

Type	Description
boolean	True if the value is a number between min and max (inclusive)

Examples

is.inRange(5, 1, 10)  // true
is.inRange(1, 1, 10)  // true
is.inRange(10, 1, 10) // true
is.inRange(0, 1, 10)  // false
is.inRange(11, 1, 10) // false

inRangeExclusive

Signature

is.inRangeExclusive (value, min, max)

Description

Check if a value is strictly within a numeric range (exclusive on both ends).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
min	number	yes	Minimum value (exclusive)
max	number	yes	Maximum value (exclusive)

Returns

Type	Description
boolean	True if the value is a number strictly between min and max

Examples

is.inRangeExclusive(5, 1, 10)  // true
is.inRangeExclusive(1, 1, 10)  // false
is.inRangeExclusive(10, 1, 10) // false

inRangeExclusiveMin

Signature

is.inRangeExclusiveMin (value, min, max)

Description

Check if a value is within a numeric range, exclusive on the lower bound and inclusive on the upper bound.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
min	number	yes	Minimum value (exclusive)
max	number	yes	Maximum value (inclusive)

Returns

Type	Description
boolean	True if min < value <= max

Examples

is.inRangeExclusiveMin(10, 1, 10) // true
is.inRangeExclusiveMin(1, 1, 10)  // false
is.inRangeExclusiveMin(5, 1, 10)  // true

inRangeExclusiveMax

Signature

is.inRangeExclusiveMax (value, min, max)

Description

Check if a value is within a numeric range, inclusive on the lower bound and exclusive on the upper bound.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
min	number	yes	Minimum value (inclusive)
max	number	yes	Maximum value (exclusive)

Returns

Type	Description
boolean	True if min <= value < max

Examples

is.inRangeExclusiveMax(1, 1, 10)  // true
is.inRangeExclusiveMax(10, 1, 10) // false
is.inRangeExclusiveMax(5, 1, 10)  // true

integer

Signature

is.integer (value)

Description

Check if a value is an integer.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an integer

Examples

is.integer(42)   // true
is.integer(0)    // true
is.integer(3.14) // false
is.integer('42') // false

positiveInteger

Signature

is.positiveInteger (value)

Description

Check if a value is an integer strictly greater than 0.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an integer > 0

Examples

is.positiveInteger(1)    // true
is.positiveInteger(42)   // true
is.positiveInteger(0)    // false
is.positiveInteger(-1)   // false
is.positiveInteger(3.14) // false

nonPositiveInteger

Signature

is.nonPositiveInteger (value)

Description

Check if a value is an integer less than or equal to 0.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an integer ≤ 0

Examples

is.nonPositiveInteger(0)  // true
is.nonPositiveInteger(-3) // true
is.nonPositiveInteger(1)  // false

negativeInteger

Signature

is.negativeInteger (value)

Description

Check if a value is an integer strictly less than 0.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an integer < 0

Examples

is.negativeInteger(-1)  // true
is.negativeInteger(-42) // true
is.negativeInteger(0)   // false
is.negativeInteger(1)   // false

nonNegativeInteger

Signature

is.nonNegativeInteger (value)

Description

Check if a value is an integer greater than or equal to 0.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an integer ≥ 0

Examples

is.nonNegativeInteger(0)  // true
is.nonNegativeInteger(5)  // true
is.nonNegativeInteger(-1) // false

array

Signature

is.array (value)

Description

Check if a value is an array.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an array

Examples

is.array([])        // true
is.array([1, 2, 3]) // true
is.array({})        // false
is.array('hello')   // false

emptyArray

Signature

is.emptyArray (value)

Description

Check if a value is an empty array.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an array with no elements

Examples

is.emptyArray([])     // true
is.emptyArray([1, 2]) // false
is.emptyArray({})     // false

nonEmptyArray

Signature

is.nonEmptyArray (value)

Description

Check if a value is an array with at least one element.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is an array with at least one element

Examples

is.nonEmptyArray([1, 2]) // true
is.nonEmptyArray([])     // false

arrayOfLength

Signature

is.arrayOfLength (value, length)

Description

Check if a value is an array of a specific length.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
length	number	yes	The expected length

Returns

Type	Description
boolean	True if the value is an array with the specified length

Examples

is.arrayOfLength([1, 2, 3], 3) // true
is.arrayOfLength([1, 2], 3)    // false
is.arrayOfLength([], 0)        // true

arrayOfLengthAtLeast

Signature

is.arrayOfLengthAtLeast (value, minLength)

Description

Check if a value is an array with at least a given number of elements.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
minLength	number	yes	Minimum number of elements (inclusive)

Returns

Type	Description
boolean	True if the value is an array with length >= minLength

Examples

is.arrayOfLengthAtLeast([1, 2, 3], 3) // true
is.arrayOfLengthAtLeast([1, 2, 3], 2) // true
is.arrayOfLengthAtLeast([1], 2)        // false

arrayOfLengthAtMost

Signature

is.arrayOfLengthAtMost (value, maxLength)

Description

Check if a value is an array with at most a given number of elements.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
maxLength	number	yes	Maximum number of elements (inclusive)

Returns

Type	Description
boolean	True if the value is an array with length <= maxLength

Examples

is.arrayOfLengthAtMost([1, 2], 3)    // true
is.arrayOfLengthAtMost([1, 2], 2)    // true
is.arrayOfLengthAtMost([1, 2, 3], 2) // false

arrayOfLengthBetween

Signature

is.arrayOfLengthBetween (value, minLength, maxLength)

Description

Check if a value is an array whose length falls within a given range (inclusive on both ends).

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
minLength	number	yes	Minimum number of elements (inclusive)
maxLength	number	yes	Maximum number of elements (inclusive)

Returns

Type	Description
boolean	True if the value is an array with minLength <= length <= maxLength

Examples

is.arrayOfLengthBetween([1, 2], 1, 3)       // true
is.arrayOfLengthBetween([1, 2, 3], 1, 3)    // true
is.arrayOfLengthBetween([], 1, 3)            // false
is.arrayOfLengthBetween([1, 2, 3, 4], 1, 3) // false

map

Signature

is.map (value)

Description

Check if a value is a Map instance.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a Map instance

Examples

is.map(new Map())           // true
is.map(new Map([['a', 1]])) // true
is.map({})                  // false
is.map(null)                // false

emptyMap

Signature

is.emptyMap (value)

Description

Check if a value is a Map instance with no entries.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a Map with no entries

Examples

is.emptyMap(new Map())           // true
is.emptyMap(new Map([['a', 1]])) // false

nonEmptyMap

Signature

is.nonEmptyMap (value)

Description

Check if a value is a Map instance with at least one entry.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a Map with at least one entry

Examples

is.nonEmptyMap(new Map([['a', 1]])) // true
is.nonEmptyMap(new Map())           // false

set

Signature

is.set (value)

Description

Check if a value is a Set instance.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a Set instance

Examples

is.set(new Set())       // true
is.set(new Set([1, 2])) // true
is.set([])              // false
is.set(null)            // false

emptySet

Signature

is.emptySet (value)

Description

Check if a value is a Set instance with no elements.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a Set with no elements

Examples

is.emptySet(new Set())       // true
is.emptySet(new Set([1, 2])) // false

nonEmptySet

Signature

is.nonEmptySet (value)

Description

Check if a value is a Set instance with at least one element.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a Set with at least one element

Examples

is.nonEmptySet(new Set([1, 2])) // true
is.nonEmptySet(new Set())       // false

function

Signature

is.function (value)

Description

Check if a value is a function.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is a function

Examples

is.function(() => {})      // true
is.function(function() {}) // true
is.function(Array.isArray) // true
is.function({})            // false

oneOf

Signature

is.oneOf(value, allowedValues)

Description

Check if a value is one of the allowed values.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check
allowedValues	Array	yes	Array of allowed values

Returns

Type	Description
boolean	True if the value is included in allowedValues

Examples

is.oneOf('red', ['red', 'green', 'blue'])    // true
is.oneOf('yellow', ['red', 'green', 'blue']) // false
is.oneOf(2, [1, 2, 3])                       // true

empty

Signature

is.empty (value)

Description

Check if a value is empty. A value is considered empty if it is null, undefined, a whitespace-only string, an empty array, an empty object, an empty Map, or an empty Set.

Parameters

Name	Type	Required	Description
value	*	yes	The value to check

Returns

Type	Description
boolean	True if the value is considered empty

Examples

is.empty(null)      // true
is.empty(undefined) // true
is.empty('')        // true
is.empty('   ')     // true
is.empty([])        // true
is.empty({})        // true
is.empty(new Map()) // true
is.empty(new Set()) // true
is.empty(0)         // false
is.empty(false)     // false
is.empty('hello')   // false