A collection of composable JavaScript runtime type predicates with TypeScript type guard declarations
Isntnt is a collection of composable JavaScript runtime type predicates with TypeScript type guard declarations. Supports generics including union and intersection types.
A predicate is a function that checks whether a value matches a certain type, it always returns a boolean. Well known examples of JavaScript predicates are Array.isArray, isNan, and Number.isNaN. With isntnt you add a whole slew of additional predicates to your toolbox, they are listed below.
Returns true when you pass an object with a length property that is a valid length.
isWithLength(value)
Always returns true.
isAny(value)
Returns true when you pass an array.
isArray(value)
Returns true when you pass a object that is not a function with a length property that is a valid length.
isArrayLike(value)
Returns true when you pass a bigint.
isBigInt(value)
Returns true when you pass a boolean.
isBoolean(value)
Returns true when you pass a Date object.
isDate(value)
Returns true when you pass an object of which each property name, and each property value are a string.
isDictionary(value)
Returns true when you pass false.
isFalse(value)
Returns true when you pass a function.
isFunction(value)
Returns true when you pass an integer (a whole number).
isInt(value)
Returns true when you pass an integer ranging from -128 to 127.
isInt8(value)
Returns true when you pass an integer ranging from -32,768 to 32,767.
isInt16(value)
Returns true when you pass an integer ranging from -2,147,483,648 to 2,147,483,647.
isInt32(value)
Alias to isUint32.
isLength(value)
Returns true when you pas a Map object.
isMap(value)
Returns true when you pas a negative number (including -0).
isNegative(value)
Always returns false.
isNever(value)
Returns true when you pass null or undefined.
isNone(value)
Returns true when you pass null.
isNull(value)
Returns true when you pass a number that is not NaN.
isNumber(value)
Returns true when you pass an object that is not null.
isObject(value)
Returns true when you pass an value that is not a boolean, null, or undefined.
isObjectLike(value)
Returns true when you pass an object that was constructed by Object.
isPlainObject(value)
Returns true when you pass a positive number.
isPositive(value)
Returns true when you pass null, undefined, a boolean, bigint, number, symbol, or string.
isPrimitive(value)
Returns true when you pass a RegExp object.
isRegExp(value)
Returns true when you pass a serializable primitive, a serializable array, or serializable object.
isSerializable(value)
Returns true when you pass an array where every element is serializable.
isSerializableArray(value)
Returns true when you pass a number that is not NaN, Infinity, or -Infinity.
isSerializableNumber(value)
Returns true when you pass an object where every property is serializable.
isSerializableObject(value)
Returns true when you pass null, a serializable number, a boolean, bigint, symbol, or string.
isSerializablePrimitive(value)
Returns true when you pas a Set object.
isSet(value)
Returns true when you pas a value other than null or undefined.
isSome(value)
Returns true when you pas a string.
isString(value)
Returns true when you pas a symbol.
isSymbol(value)
Returns true when you pas true.
isTrue(value)
Returns true when you pass a positive integer.
isUint(value)
Returns true when you pass an unsigned integer ranging from 0 to 255.
isUint8(value)
Returns true when you pass an unsigned integer ranging from 0 to 65,535.
isUint16(value)
Returns true when you pass an unsigned integer ranging from 0 to 4,294,967,295.
isUint32(value)
Returns true when you pass undefined.
isUndefined(value)
Returns true when you pass a WeakMap object.
isWeakMap(value)
Predicate factories is where the real fun begins, they allow you to create and combine predicates of your own to create new predicates. By composing predicates you can describe objects, union types, number ranges, and so on.
Create a predicate based on a floor value, it checks if a number exceeds the floor value it’s given. This is an analogue to the > operator.
const isAboveZero = above(0)
isAboveZero(-1) // false
isAboveZero(12) // true
The isAboveZero predicate above returns true when you pass a number that is greater than 0.
Create a predicate based on several other predicates, it returns true if every predicate that is passed also returns true. This is an analogue to the && operator.
const adultAge = 18
const isMinorAge = and(isUint, below(adultAge))
isMinorAge(12) // true
isMinorAge(33) // false
The isMinorAge predicate above returns true when you pass an unsigned integer that is below 18.
const isUser = shape({ name: isString })
const hasEmailAddress = shape({ email: isString })
const isUserWithEmail = and(isUser, hasEmailAddress)
The isUserWithEmail predicate above returns true when you pass an object with a name and an email property, both of which are a string.
Create a predicate that checks every array element, it returns true when its predicate returns true for every element in an array.
const isNumberArray = array(isNumber)
The isNumberArray predicate above returns true when you pass an array of which every element is a number.
Create a predicate based on a property key and another predicate, it returns true when its predicate returns true for the value of an object at its given key.
const isStringAtName = at('name', isString)
isStringAtName({ name: 'Jane' }) // true
isStringAtName({ name: null }) // false
The isStringAtName predicate above returns true when you pass an object of which the name property is a string.
Create a predicate based on a ceiling value, it checks if a number is below the ceiling value it’s given. This is an analogue to the < operator.
const isBelow100 = below(100)
isBelow100(124) // false
isBelow100(32) // true
The isBelow100 predicate above returns true when you pass a number that is less than 100.
Create a predicate based on several literal values, it returns true if a value matches either of the primitive values it’s given.
const isAOrB = either('a', 'b')
isAOrB('a') // true
isAOrB('c') // false
The isAOrB predicate above returns true when you pass either a, or b.
Create a predicate based on a property key, it returns true if an object has a property of the key it’s given.
const hasName = has('name')
hasName({ name: null }) // true
hasName({ age: 36 }) // false
The hasName predicate above returns true when you pass an object that has a name property.
Create a predicate based on a constructor, it returns true if an object is an instance of the constructor key it’s given.
const isInstanceofString = instance(String)
isInstanceofString(new String('foo')) // true
isInstanceofString('foo') // false
The isInstanceofString predicate above returns true when you pass a String object.
Create a predicate based a primitive value, it returns true if a value equals the primitive value it’s given.
const is42 = literal(42)
is42(42) // true
is42(43) // false
The is42 predicate above returns true when you pass 42.
Create a predicate based on a max. value, it checks if a number is below or equal to the max. value it’s given. This is an analogue to the <= operator.
const isMax100 = max(100)
isMax100(100) // true
isMax100(101) // false
The isMax100 predicate above returns true when you pass a number that is below or equal to 100.
Create a predicate based on another predicate, it checks if a value matches it’s given predicate, or equals null or undefined.
const isMaybeString = maybe(isString)
isMaybeString(null) // true
isMaybeString(12) // false
The isMaybeString predicate above returns true when you pass a string, null, or undefined.
Create a predicate based on a min. value, it checks if a number is above or equal to the min. value it’s given. This is an analogue to the >= operator.
const isMin100 = min(100)
isMin100(100) // true
isMin100(99) // false
The isMin0 predicate above returns true when you pass a number that is above or equal to 100.
Aliases maybe.
Create a predicate based on another predicate, it checks if a value matches it’s given predicate, or equals null.
const isNullableString = nullable(isString)
isNullableString(null) // true
isNullableString(12) // false
The isNullableString predicate above returns true when you pass a string or null.
Create a predicate that checks every object property, it returns true when its predicate returns true for every object value.
const isEnumerable = object(isUint)
The isEnumerable predicate above returns true when you pass an object of which every element is an unsigned integer.
<T>(predicate: Predicate<T>) => (value: unknown) => value is T | undefined
const isOptionalString = optional(isString)
isOptionalString(undefined) // true
isOptionalString(12) // false
The isOptionalString predicate above returns true when you pass a string or undefined.
Create a predicate based on several other predicates, it returns true if some predicate that is passed also returns true. This is an analogue to the || operator.
const isContent = or(isString, isSerializableNumber)
isContent(12) // true
isContent(null) // false
The isContent predicate above returns true when you pass a string or a primitive number.
const isStringOrNumber = or(isString, isNumber)
isStringOrNumber(8) // true
isStringOrNumber([]) // false
Create a predicate based on a key predicate and a value predicate, it returns true if each property key of an object returns true for its key predicate, and each value returns true for its value predicate.
const isValidKey = either('a', 'b')
const isKeyValueMap = record(isValidKey, isInt)
isKeyValueMap({ a: 2 }) // true
isKeyValueMap({ a: null }) // false
isKeyValueMap({ c: 2 }) // false
The isKeyValueMap predicate above returns true when you pass an object where each key is either a or b, and each property value is an integer.
Create a predicate based on a predicate object, it returns true if each property value of an object returns true for its corresponding predicate.
const isPoint = shape({ x: isNumber, y: isNumber })
isPoint({ x: 12, y: 36 }) // true
isPoint({ x: 12 }) // false
The isPoint predicate above returns true when you an pass an object where both x and y properties are a number.
const isSlug = test(/^[A-Z0-9-]+$/i)
isSlug('foo-bar') // true
isSlug('!#$') // false
The isSlug predicate above returns true when you an pass a string that matches /^[A-Z0-9-]+$/i.
Create a predicate based on index-based predicates, it returns true if the element at each index of an array with a fixed length returns true for its corresponding predicate.
const isLatitude = and(min(-90), max(90))
const isLongitude = and(min(-180), max(180))
const isLatLong = tuple(isLatitude, isLongitude)
isLatLong(45, -120) // true
isLatLong(120, 200) // false
The isLatLong predicate above returns true when you an pass an array with a length of 2 where index 0 is a latitude, and index 1 is a longitude value.
type User = Intersect<{ name: string } | { email: string }>
equals
type User = {
name: string
} & {
email: string
}
Unions a type with null and undefined.
type MaybeString = Maybe<string>
equals
type MaybeString = string | null | undefined
Union of null and undefined.
type NoneType = None
equals
type NoneType = null | undefined
Unions a type with null.
type NullableString = Nullable<string>
equals
type NullableString = string | null
Unions a type with undefined.
type OptionalString = Optional<string>
equals
type OptionalString = string | undefined
Describes a predicate function signature
type IsString = Predicate<string>
equals
type IsString = <T>(value: T) => value is Extract<T, string>
Union of all primitive types.
type PrimitiveType = Primitive
equals
type PrimitiveType = null | undefined | boolean | number | string | symbol | bigint
type SerializableType = Serializable
equals
type SerializableType = SerializableArray | SerializableObject | SerializableObject
type SerializableArrayType = SerializableArray
equals
type SerializableArrayType = Array<Serializable> | ReadonlyArray<Serializable>
type SerializableObjectType = SerializableObject
equals
type SerializableObjectType = { [key: string]: Serializable | undefined }
type SerializablePrimitiveType = SerializablePrimitive
equals
type SerializablePrimitiveType = null | boolean | number | string
Excludes null and undefined from type.
type SomeType = Some
type SomeString = Some<string | null>
equals
type SomeType = Function | boolean | bigint | number | string | symbol | object
type SomeString = string
Extracts type parameter from Predicate type. This is useful to extract TypeScript types from (complex) predicates.
type PredicateType = Static<Predicate<string>>>
equals
type PredicateType = string
FAQs
A collection of composable JavaScript runtime type predicates with TypeScript type guard declarations
The npm package isntnt receives a total of 432 weekly downloads. As such, isntnt popularity was classified as not popular.
We found that isntnt demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 11 open source maintainers collaborating on the project.
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