type-plus
Advanced tools
More than 200 type utilities for TypeScript.
npm install type-plus
yarn add type-plus
pnpm add type-plus
Assertion Functions are special functions that asserts certain conditions of your program.
It is introduced in TypeScript 3.7.
They throw an error if the condition is not met, and return nothing otherwise.
These assertion functions are typically used in runtime, so that that type of the value can be narrowed down.
assertType provides a generic assertion function,
as well as many assertion functions for builtin types.
💀 deprecated. Use assertType.as() instead.
assertType<T>(subject, validator):
🚦assertion: assert the subject is type T with the specified validator.
If subject fails the assertion,
a standard TypeError will be thrown and provide better error info.
For example:
const s: unknown = 1
// TypeError: subject fails to satisfy s => typeof s === 'boolean'
assertType<boolean>(s, s => typeof s === 'boolean')
The message beautification is provided by tersify.
🚦assertion: assert the subject is undefined.
🚦assertion: assert the subject is not undefined.
🚦assertion: assert the subject is null.
🚦assertion: assert the subject is not null.
🚦assertion: assert the subject is number.
🚦assertion: assert the subject is not number.
🚦assertion: assert the subject is boolean.
🚦assertion: assert the subject is not boolean.
🚦assertion: assert the subject is true.
🚦assertion: assert the subject is not true.
🚦assertion: assert the subject is false.
🚦assertion: assert the subject is not false.
🚦assertion: assert the subject is string.
🚦assertion: assert the subject is not string.
🚦assertion: assert the subject is function.
🚦assertion: assert the subject is not function.
🚦assertion: assert the subject is an Error.
🚦assertion: assert the subject is not an Error.
💀 deprecated. It does not work in all cases.
It passes for function that can be called with new.
If the subject is an arrow function, it can still return true after compilation.
🚦assertion: assert the subject is never.
🚦assertion: creates a custom assertion function.
Using it to create a custom assertion function that provides better error messages.
The message beautification is provided by tersify.
🚦assertion: assert the subject as T without validator.
This works similar to manual assertion ;(subject as T)
User-defined type guard functions is a function which its return type is specified as x is T.
🛡️ guard: a generic type guard function
💀 deprecated: use testType.true() instead.
💀 deprecated: use testType.false() instead.
💀 deprecated: use testType.never() instead.
💀 deprecated: use testType.equal() instead.
Equal<A, B, Then = true, Else = false>
💀 deprecated. use IsEqual instead. This will be converted to a ↪️ parse.
IsEqual<A, B, Then = true, Else = false>
⭕ predicate: if A and B are the same.
NotEqual<A, B, Then = true, Else = false>
💀 deprecated. use IsNotEqual instead. This will be converted to a ↪️ parse.
IsNotEqual<A, B, Then = true, Else = false>:
⭕ predicate: check if A and B are not the same.
Extendable<A, B, Then = A, Else = never>
↪️ parse: check if A extends B.
IsExtend<A, B, Then = true, Else = false>
⭕ predicate: check if A extends B.
NotExtendable<A, B, Then = A, Else = never>:
↪️ parse: check if A not extends B.
IsNotExtend<A, B, Then = true, Else = false>:
⭕ predicate: check if A not extends B.
IsAssign<A, B, Then = true, Else = false>
💀 deprecated: use CanAssign instead.
CanAssign<A, B, Then = true, Else = false>:
⭕ predicate: check can A assign to B.
A typical usage is using it with assertType:
assertType.isFalse(false as CanAssign<boolean, { a: string }>)
assertType.isTrue(true as CanAssign<{ a:string, b:number }, { a: string }>)
StrictCanAssign<A, B, Then = true, Else = false>
⭕ predicate: can A strictly assign to B
When A is a union, all branches must be assignable to B.
StrictCanAssign<number | string, number> // false
StrictCanAssign<number | string, number | string> // true
canAssign<T>(): (subject) => true
⭕💻 predicate, compile-time
Returns a compile-time validating function to ensure subject is assignable to T.
const isConfig = canAssign<{ a: string }>()
assertType.isTrue(isConfig({ a: 'a' }))
canAssign<T>(false): (subject) => false:
⭕💻 predicate, compile-time
Returns a compile-time validating function to ensure subject is not assignable to T.
const notA = canAssign<{ a: string }>(false)
assertType.isTrue(notA({ a: 1 }))
notA({ a: '' }) // TypeScript complains
type-plus privides type checking utilities for every type.
Each type has at least 4 type checks.
Using string as an example, there are StringType<T>, IsString<T>, NotStringType<T>, and IsNotString<T>.
Some types will have more checks, such as boolean has StrictBooleanType<T>, TrueType<T>, FalseType<T>.
You can learn more in their respective sections:
↪️ parse: T === any.
⭕ predicate: T === any.
↪️ parse: T !== any.
⭕ predicate: T !== any.
⭕ predicate: T === any || T === never.
↪️ parse: is the type T exactly an array and not a tuple.
⭕ predicate: is the type T exactly an array and not a tuple.
↪️ parse: is the type T not an array or tuple.
⭕ predicate: is the type T exactly an array and not a tuple.
🔨 utilities: gets the element type at index N in the array A.
CommonPropKeys<A>
🔨 utilities: gets common keys inside the records in the array A (deprecate CommonKeys).
🔨 utilities: [...A, ...B].
CreateTuple<L, T>
🔨 utilities: creates tuple<T> with L number of elements.
drop(array, value)
🔨 utilities: drop a particular value from an array.
DropFirst<A>
🔨 utilities: drops the first value type of A.
DropLast<A>
🔨 utilities: drops the last value type of A.
DropMatch<A, Criteria>
🔨 utilities: drops entries matching Criteria in array or tuple A.
DropUndefined<A>
🔨 utilities: drop undefined entries from array of tuple A.
Filter<A, Criteria>
💀🔨 deprecated,utilities: filter the array or tuple A, keeping entries satisfying Criteria. Deprecated. Renaming to KeepMatch
FindFirst<A, Criteria>
🔨 utilities: gets the first type satisfying Criteria.
FindLast<A, Criteria>
🔨 utilities: gets the last type satisfying Criteria.
Head<A>
🔨 utilities: gets the first entry in the array.
IntersectOfProps<A, K>
🔨 utilities: gets the intersect of A[K] types (deprecate MapToProp)
KeepMatch<A, Criteria>
🔨 utilities: keeps entries satisfying Criteria in array or tuple A.
Last<A>
🔨 utilities: gets the last type of array or tuple.
literalArray(...entries)
🔨 utilities: return an array whose items are restricted to the provided literals.
PadLeft<A, Total, PadWith>
🔨 utilities: pads A with PadWith if the length of A is less than L.
reduceWhile()
🔨 utilities: reduce() with predicate for early termination.
A simple version of the same function in the ramda package.
Reverse<A>
🔨 utilities: reverses the order of A.
Some<A, Criteria>
🔨 utilities: true if some elements in A matches Criteria.
Tail<A>
🔨 utilities: Gets the types of a tuple except the first entry.
UnionOfProps<A, K>
🔨 utilities: gets the union of A[K] types (deprecate PropUnion).
UnionOfValues<A>
🔨 utilities: gets the union of value types in A (deprecate ArrayValue).
🔨 utilities: gets the normalized index for A.
ArrayPlus.IsIndexOutOfBound<A, N, Then = true, Else = false>
⭕ predicate: is N an out of bound index of A. Supports negative numbers.
↪️ parse: if T is bigint or bigint literal.
⭕ predicate: if T is bigint or bigint literal.
↪️ parse: if T is not bigint or bigint literal.
⭕ predicate: if T is not bigint or bigint literal.
↪️ parse: if T is exactly bigint.
⭕ predicate: if T is exactly bigint.
↪️ parse: if T is not exactly bigint.
⭕ predicate: if T is not exactly bigint.
↪️ parse: T === boolean.
⭕ predicate: T === boolean
↪️ parse: T !== boolean.
⭕ predicate: T !== boolean
↪️ parse: T === function.
⭕ predicate: T === function
↪️ parse: T !== function.
⭕ predicate: T !== function
AnyFunction<P, R>
🔨 utilities: a generic type for any function
ExtractFunction<F>
🔨 utilities: extract the function signature from a type F.
extractFunction(fn: F)
🔨 utilities: adjust type of fn to its function signature only.
inspect<T>(value: T, inspector?: (v: T) => void)
🔨 utilities: inspect a value and return it. Inspector defaults to console.dir()
↪️ parse: T === never.
⭕ predicate: T === never
↪️ parse: T !== never.
⭕ predicate: T !== never
↪️ parse: T === null.
⭕ predicate: T === null
↪️ parse: T !== null.
⭕ predicate: T !== null
↪️ parse: is the type T number.
⭕ predicate: is the type T number.
↪️ parse: is the type T not number.
⭕ predicate: is the type T not number.
↪️ parse: is the type T exactly number.
⭕ predicate: is the type T exactly number.
↪️ parse: is the type T not exactly number.
⭕ predicate: is the type T not exactly number.
📘 definition: number | bigint.
📘 definition: 0 | 0n
↪️ parse: is integer.
⭕ predicate: is integer.
↪️ parse: is not integer.
⭕ predicate: is not integer.
💀⭕ deprecated, predicate: is integer. Use IsInteger instead.
↪️ parse: is negative.
⭕ predicate: is negative.
↪️ parse: is not negative.
⭕ predicate: is not negative.
↪️ parse: is positive.
⭕ predicate: is positive.
↪️ parse: is not positive.
⭕ predicate: is not positive.
filterKey()
🔨 utilities: type adjusted filter by key.
findKey()
🔨 utilities: type adjusted find by key.
forEachKey()
🔨 utilities: type adjusted for each by key.
HasKey<T, K>
🔨 utilities: predicate type checking T has key K.
hasKey()
🔨 utilities: function of HasKey.
IsRecord<T>
🔨 utilities: logical predicate for Record.
KeysWithDiffTypes<A, B>
🔨 utilities: gets the keys common in A and B but with different value type.
mapKey()
🔨 utilities: type adjusted map by key.
RecordValue<R>
🔨 utilities: gets the value type Tfrom Record<any, T>
reduceByKey()
🔨 utilities: type adjusted reduce by key.
someKey()
🔨 utilities: type adjusted some by key.
SpreadRecord<A, B>
🔨 utilities: type for {...a, ...b} when both a and b are Record
for array, just do [...A, ...B].
AwaitedProp<T, V>
🔨 utilities: Awaited on specified props P in T.
isPromise<R>(subject: any)
🔨 utilities: isPromise() type guard.
MaybePromise<T>
🔨 utilities: Alias of T | Promise<T>.
PromiseValue<P>
🔨 utilities: Gets the type within the Promise.
PromiseValueMerge<P1, P2, ...P9>
🔨 utilities: Merge the values of multiple promises.
mapSeries()
🔨 utilities: Similar to bluebird.mapSeries() but works with async/await.
transformMaybePromise(value, transformer)
🔨 utilities: Apply the transformer to the value.
It is also exported under MaybePromise.transform().
↪️ parse: is string.
⭕ predicate: is string.
↪️ parse: is not string.
⭕ predicate: is not string.
↪️ parse: is symbol.
⭕ predicate: is symbol.
↪️ parse: is not symbol.
⭕ predicate: is not symbol.
↪️ parse: is a tuple.
⭕ predicate: is a tuple.
↪️ parse: is not a tuple.
⭕ predicate: is not a tuple.
↪️ parse: T === undefined.
⭕ predicate: T === undefined
↪️ parse: T !== undefined.
⭕ predicate: T !== undefined
↪️ parse: T === unknown.
⭕ predicate: T === unknown
↪️ parse: T !== unknown.
⭕ predicate: T !== unknown
↪️ parse: T === void.
⭕ predicate: T === void
↪️ parse: T !== void.
⭕ predicate: T !== void
KeyTypes
📘 definition: type of all keys.
PrimitiveTypes
📘 definition: all primitive types, including Function, symbol, and bigint.
ComposableTypes
📘 definition: Types that can contain custom properties. i.e. object, array, function.
NonComposableTypes
📘 definition: Types that cannot contain custom properties. i.e. not composable.
JSONPrimitive
📘 definition: primitive types valid in JSON
JSONObject
📘 definition: JSON object
JSONArray
📘 definition: JSON array
JSONTypes
📘 definition: all JSON compatible types.
JSONTypes.get<T>(obj, ...props)
🔨 utilities: get a cast value in JSON
import { JSONTypes } from 'type-plus'
const someJson: JSONTypes = { a: { b: ['z', { c: 'miku' }]}}
JSONTypes.get<string>(someJson, 'a', 'b', 1, 'c') // miku
ANotB<A, B>
🔨 utilities: get object with properties in A and not in B, including properties with a different value type.
BNotA<A, B>
🔨 utilities: flip of ANotB
as<T>(subject)
🔨 utilities: assert subject as T. Avoid ASI issues such as ;(x as T).abc
asAny(subject)
🔨 utilities: assert subject as any. Avoid ASI issue such as ;(x as any).abc
EitherAnd<A, B, [C, D]>
💀🔨 deprecated,utilities: Renamed to EitherOrBoth. combines 2 to 4 types as A | B | (A & B).
This is useful for combining options.
EitherOrBoth<A, B, [C, D]>
🔨 utilities: combines 2 to 4 types as A | B | (A & B).
This is useful for combining options video.
Except<T, K>
💀🔨 deprecated,utilities: same as Omit<T, K>.
ExcludePropType<T, U>
🔨 utilities: excludes type U from properties in T.
KeyofOptional<T>
🔨 utilities: keyof that works with Record<any, any> | undefined.
KnownKeys<T>
🔨 utilities: extract known (defined) keys from type T.
LeftJoin<A, B>
🔨 utilities: left join A with B
NonNull<T>
🔨 utilities: remove null
NonNullable<T>(built-in)
🔨 utilities: adjust the type not to nullable
NonUndefined<T>
🔨 utilities: remove undefined
Omit<T, K>
🔨 utilities: From T, pick a set of properties whose keys are not in the union K. This is the opposite of Pick<T, K>.
OptionalKeys<T>
🔨 utilities: gets keys of optional properties in T.
PartialExcept<T, U>
💀🔨 deprecated,utilities: same as PartialOmit<T, U>.
PartialOmit<T, U>
🔨 utilities: makes the properties not specified in U becomes optional.
PartialPick<T, U>
🔨 utilities: makes the properties specified in U becomes optional.
Pick<T, K>
🔨 utilities: pick properties K from T. Works with unions.
RecursivePartial<T>
🔨 utilities: make type T optional recursively.
RecursiveRequired<T>
🔨 utilities: make type T required recursively.
ReplaceProperty<T, K, V>
🔨 utilities: replace property K in T with V.
RequiredKeys<T>
🔨 utilities: gets keys of required properties in T.
RequiredPick<T, U>
🔨 utilities: makes the properties specified in U become required.
RequiredExcept<T, U>
🔨 utilities: makes the properties not specified in U become required.
RecursiveIntersect<T, U>
🔨 utilities: intersect type U onto T recursively.
ValueOf<T>
🔨 utilities: type of the value of the properties of T.
Widen<T>
🔨 utilities: widen literal types.
PropType
💀 ...no helper type for this. Just do YourType['propName'].
Type predicates are type alias that returns true or false.
They can be used to compose complex types.
HasKey<T, K>
🔨 utilities: predicate type checking T has key K.
IsAny<T>
🔨 utilities: T === any (updated to impl: expect-type).
IsBoolean<T>
🔨 utilities: check for boolean, but not for true nor false.
IsDisjoint<A, B>
🔨 utilities: is A and B is a disjoint set.
IsEmptyObject<T>
🔨 utilities: is T === {}.
IsLiteral<T>
🔨 utilities: is T a literal type (literal string or number).
If<Condition, Then = true, Else = false>
🔨 utilities: if statement
And<A, B, Then = true, Else = false>
🔨 utilities: logical AND
Or<A, B, Then = true, Else = false>
🔨 utilities: logical OR
Xor<A, B, Then = true, Else = false>
🔨 utilities: logical XOR
Not<X, Then = true, Else = false>
🔨 utilities: logical NOT
Note that these types work correctly with the boolean type.
e.g.:
type R = And<boolean, true> // boolean
type R = Not<boolean> // boolean`
There is a problem with generic distribution: https://github.com/microsoft/TypeScript/issues/41053 So you may encounter some weird behavior if your logic is complex.
The math types in type-plus works with most numeric types.
It works with number and bigint, positive and negative number, including floating point numbers.
It will cast the type between number and bigint if needed.
Abs<N, Fail = never>
🔨 utilities: Abs(N).
Max<A, B, Fail = never>
🔨 utilities: max(A, B)
GreaterThan<A, B>
🔨 utilities: A > B.
Add<A, B>
🔨 utilities: A + B.
Subtract<A, B>
🔨 utilities: A > B.
Increment<A>
🔨 utilities: alias of Add<A, 1>.
Decrement<A>
🔨 utilities: alias of Subtract<A, 1>.
Multiply<A, B
🔨 utilities: A * B.
amend(subject)...
🔨 utilities: amend subject as union or intersect of T.
facade(subject, ...props)
🔨 utilities: create a facade of subject.
getField(subject, key, defaultValue)
🔨 utilities: get a field from a subject. Works against nullable and optional subject.
hasKey()
🔨 utilities: function of HasKey.
hasProperty(value, prop)
🔨 utilities: assert value has property prop. This will pick the correct union type.
isConstructor(subject)
🔨 utilities: type guard subject is a constructor.
isSystemError(code, err)
🔨 utilities: type guard err with NodeJS error code.
omit(obj, ...props)
🔨 utilities: omit properties from obj.
pick(obj, ...props)
🔨 utilities: pick properties from obj.
record<K, V>(value?)
🔨 utilities: create a Record<K, V> without extra object prototype.
record<R>(value?)
🔨 utilities: create a record R (e.g. { a: number }) without extra object prototype.
required(...)
🔨 utilities: merge options and remove Partial<T>. From unpartial
requiredDeep(...)
🔨 utilities: merge options deeply and remove Partial<T>. From unpartial
split(target, ...splitters)
🔨 utilities: split one object into multiple objects.
stub<T>(value)
🔨 utilities: stub a particular type T.
stub.build<T>(init?)
🔨 utilities: build a stub for particular type T.
typeOverrideIncompatible<T>()
🔨 utilities: override only the incompatible portion between two types.
type A = {
foo: boolean,
bar: string,
baz: string
}
const overrider = typeOverrideIncompatible<A>()
const source = {
foo: 1,
bar: 'bar',
baz: 'baz'
}
// only the `foo` property is available to override.
overrider(source, { foo: !!source.foo })
unpartial()
🔨 utilities: merge options and remove Partial<T> values. From unpartial
context()
🔨 utilities: a context builder.
This is useful to build context for functional programming.
It is a sync version of the AsyncContext from async-fp.
import { context } from 'type-plus'
// { a: 1, b: 2 }
const ctx = context({ a: 1 })
.extend(c => ({ b: c.a + 1 }))
.build()
The TypeScript type system is structural.
In some cases, we want to express a type with nominal behavior.
type-plus provides two kinds of nominal types: Brand and Flavor.
Brand<B, T>:
brand(type, subject?):
Branded nominal type is the stronger nominal type of the two. It disallows unbranded type assigned to it:
const a = brand('a', { a: 1 })
const b = { a: 1 }
a = b // error
subject can be any type, from primitive to strings to objects.
brand(type):
If you do not provide subject, brand(type) will return a brand creator,
so that you can use it to create multiple branded values:
const nike = brand('nike')
const shirt = nike('shirt')
const socks = nike('socks')
Flavor<F, T>:
flavor(type, subject?):
The key difference between Flavor and Brand is that
unflavored type can be assigned to Flavor:
let f = flavor('orange', 'soda')
f = 'mist' // ok
Also, Brand of the same name can be assigned to Flavor,
but Flavor of the same name cannot be assigned to Brand.
nominalMatch(a, b):
🔨 utilities: compare if the two values are nominally equal.
Works with both Brand and Flavor.
const b1 = brand('x', 1)
const b2 = brand('y', 1)
nominalMatch(b1, b2) // false
ChainFn<T>: T
🔨 utilities: chain function that returns the input type.
compose(...fns): F
🔨 utilities: compose functions
Some code in this library is created by other people in the TypeScript community. I'm merely adding them in and maybe making some adjustments. Whenever possible, I add attribution to the person who created those codes in the file.
Pipe.FAQs
Provides additional types for TypeScript.
The npm package type-plus receives a total of 17,804 weekly downloads. As such, type-plus popularity was classified as popular.
We found that type-plus demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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