A collection of essential TypeScript types
Many of the types here should have been built-in. You can help by suggesting some of them to the TypeScript project.
Either add this package as a dependency or copy-paste the needed types. No credit required. 👌
PR welcome for additional commonly needed types and docs improvements. Read the contributing guidelines first.
Help wanted with reviewing proposals and pull requests.
Install
npm install type-fest
Requires TypeScript >=5.9, ESM, and {strict: true} in your tsconfig.
[!NOTE]
This readme shows the current development version. For docs about the latest version, see the npm page.
You may also like my ts-extras package which provides runtime functions for some of these types.
Usage
import type {Except} from 'type-fest';
type Foo = {
unicorn: string;
rainbow: boolean;
};
type FooWithoutRainbow = Except<Foo, 'rainbow'>;
//=> {unicorn: string}
API
Click the type names for complete docs.
Basic
Utilities
EmptyObject - Represents a strictly empty plain object, the {} value.NonEmptyObject - Represents an object with at least 1 non-optional key.UnknownRecord - Represents an object with unknown value. You probably want this instead of {}.UnknownArray - Represents an array with unknown value.UnknownMap - Represents a map with unknown key and value.UnknownSet - Represents a set with unknown value.Except - Create a type from an object type without certain keys.Writable - Create a type that strips readonly from the given type. Inverse of Readonly<T>.WritableDeep - Create a deeply mutable version of an object/ReadonlyMap/ReadonlySet/ReadonlyArray type. The inverse of ReadonlyDeep<T>. Use Writable<T> if you only need one level deep.Merge - Merge two types into a new type. Keys of the second type overrides keys of the first type.ObjectMerge - Merge two object types into a new object type, where keys from the second override keys from the first.MergeDeep - Merge two objects or two arrays/tuples recursively into a new type.MergeExclusive - Create a type that has mutually exclusive keys.OverrideProperties - Override existing properties of the given type. Similar to Merge, but enforces that the original type has the properties you want to override.RenameKeys - Rename keys in an object type according to a map of old-to-new names.RequireAtLeastOne - Create a type that requires at least one of the given keys, while keeping the remaining keys as is.RequireExactlyOne - Create a type that requires exactly one of the given keys and disallows more, while keeping the remaining keys as is.RequireAllOrNone - Create a type that requires all of the given keys or none of the given keys, while keeping the remaining keys as is.RequireOneOrNone - Create a type that requires exactly one of the given keys or none of the given keys, while keeping the remaining keys as is.SingleKeyObject - Create a type that only accepts an object with a single key.RequiredDeep - Create a deeply required version of another type.PickDeep - Pick properties from a deeply-nested object.OmitDeep - Omit properties from a deeply-nested object.OmitIndexSignature - Omit any index signatures from the given object type, leaving only explicitly defined properties.PickIndexSignature - Pick only index signatures from the given object type, leaving out all explicitly defined properties.PartialDeep - Create a deeply optional version of another type.PartialOnUndefinedDeep - Create a deep version of another type where all keys accepting undefined type are set to optional.UndefinedOnPartialDeep - Create a deep version of another type where all optional keys are set to also accept undefined.UnwrapPartial - Revert the Partial modifier on an object type.UnwrapRequired - Revert the Required modifier on an object type.ReadonlyDeep - Create a deeply immutable version of another type.LiteralUnion - Create a union type by combining primitive types and literal types without sacrificing auto-completion in IDEs for the literal type part of the union.Tagged - Create a tagged type that can support multiple tags and per-tag metadata.UnwrapTagged - Get the untagged portion of a tagged type created with Tagged.InvariantOf - Create an invariant type, which is a type that does not accept supertypes and subtypes.SetOptional - Create a type that makes the given keys optional, while keeping the remaining keys as is.SetReadonly - Create a type that makes the given keys readonly, while keeping the remaining keys as is.SetRequired - Create a type that makes the given keys required, while keeping the remaining keys as is.SetRequiredDeep - Create a type that makes the given keys required, with support for deeply nested key paths, while keeping the remaining keys as is.SetNonNullable - Create a type that makes the given keys non-nullable, while keeping the remaining keys as is.SetNonNullableDeep - Create a type that makes the specified keys non-nullable (removes null and undefined), supports deeply nested key paths, and leaves all other keys unchanged.NonNullableDeep - Recursively removes null and undefined from the specified type.ValueOf - Create a union of the given object's values, and optionally specify which keys to get the values from.ConditionalKeys - Extract the keys from a type where the value type of the key extends the given Condition.ConditionalPick - Pick keys from the shape that matches the given Condition.ConditionalPickDeep - Pick keys recursively from the shape that matches the given condition.ConditionalExcept - Exclude keys from a shape that matches the given Condition.UnionToIntersection - Convert a union type to an intersection type.LiteralToPrimitive - Given a literal type return the primitive type it belongs to, or never if it's not a primitive.LiteralToPrimitiveDeep - Like LiteralToPrimitive except it converts literal types inside an object or array deeply.Stringified - Create a type with the keys of the given type changed to string type.IterableElement - Get the element type of an Iterable/AsyncIterable. For example, Array, Set, Map, generator, stream, etc.Entry - Create a type that describes a single key-value pair produced when calling a collection’s entries method.Entries - Create a type that describes the key-value pairs produced when calling a collection’s entries method.SetReturnType - Create a function type with a return type of your choice and the same parameters as the given function type.SetParameterType - Create a function that replaces some parameters with the given parameters.Simplify - Useful to flatten the type output to improve type hints shown in editors. And also to transform an interface into a type to aide with assignability.SimplifyDeep - Deeply simplifies an object type.Get - Get a deeply-nested property from an object using a key path, like Lodash's .get() function.KeyAsString - Get keys of the given type as strings.Schema - Create a deep version of another object type where property values are recursively replaced into a given value type.Exact - Create a type that does not allow extra properties, meaning it only allows properties that are explicitly declared.KeysOfUnion - Create a union of all keys from a given type, even those exclusive to specific union members.OptionalKeysOf - Extract all optional keys from the given type.HasOptionalKeys - Returns a boolean for whether the given type has any optional fields.RequiredKeysOf - Extract all required keys from the given type.HasRequiredKeys - Returns a boolean for whether the given type has any required fields.ReadonlyKeysOf - Extract all readonly keys from the given type.HasReadonlyKeys - Returns a boolean for whether the given type has any readonly fields.WritableKeysOf - Extract all writable keys from the given type.HasWritableKeys - Returns a boolean for whether the given type has any writable fields.Spread - Mimic the type inferred by TypeScript when merging two objects or two arrays/tuples using the spread syntax.IsEqual - Returns a boolean for whether the two given types are equal.TaggedUnion - Create a union of types that share a common discriminant property.IntRange - Generate a union of numbers between a specified start (inclusive) and end (exclusive), with an optional step.IntClosedRange - Generate a union of numbers between a specified start and end (both inclusive), with an optional step.ArrayIndices - Provides valid indices for a constant array or tuple.ArrayValues - Provides all values for a constant array or tuple.ArraySplice - Create a new array type by adding or removing elements at a specified index range in the original array.ArrayTail - Extract the type of an array or tuple minus the first element.SetFieldType - Create a type that changes the type of the given keys.Paths - Generate a union of all possible paths to properties in the given object.SharedUnionFields - Create a type with shared fields from a union of object types.SharedUnionFieldsDeep - Create a type with shared fields from a union of object types, deeply traversing nested structures.AllUnionFields - Create a type with all fields from a union of object types.DistributedOmit - Omits keys from a type, distributing the operation over a union.DistributedPick - Pick keys from a type, distributing the operation over a union.And - Returns a boolean for whether two given types are both true.Or - Returns a boolean for whether either of two given types is true.Xor - Returns a boolean for whether only one of two given types is true.AndAll - Returns a boolean for whether all of the given elements are true.OrAll - Returns a boolean for whether any of the given elements is true.AllExtend - Returns a boolean for whether every element in an array type extends another type.SomeExtend - Returns a boolean for whether some element in an array type extends another type.NonEmptyTuple - Matches any non-empty tuple.NonEmptyString - Matches any non-empty string.FindGlobalType - Tries to find the type of a global with the given name.FindGlobalInstanceType - Tries to find one or more types from their globally-defined constructors.ConditionalSimplify - Simplifies a type while including and/or excluding certain types from being simplified.ConditionalSimplifyDeep - Recursively simplifies a type while including and/or excluding certain types from being simplified.ExclusifyUnion - Ensure mutual exclusivity in object unions by adding other members’ keys as ?: never.Optional - Create a type that represents either the value or undefined, while stripping null from the type.UnionMember - Returns an arbitrary member of a union type.UnionLength - Returns the length of a union type.
Type Guard
If - An if-else-like type that resolves depending on whether the given boolean type is true or false.IsLiteral - Returns a boolean for whether the given type is a literal type.IsStringLiteral - Returns a boolean for whether the given type is a string literal type.IsNumericLiteral - Returns a boolean for whether the given type is a number or bigint literal type.IsBooleanLiteral - Returns a boolean for whether the given type is a true or false literal type.IsSymbolLiteral - Returns a boolean for whether the given type is a symbol literal type.IsAny - Returns a boolean for whether the given type is any.IsNever - Returns a boolean for whether the given type is never.IsUnknown - Returns a boolean for whether the given type is unknown.IsEmptyObject - Returns a boolean for whether the type is strictly equal to an empty plain object, the {} value.IsNull - Returns a boolean for whether the given type is null.IsUndefined - Returns a boolean for whether the given type is undefined.IsTuple - Returns a b
type-fest is a collection of essential TypeScript types — helper types the author feels should have been built into the language, covering objects, unions, strings, arrays, tuples and functions.