Appendix B. Type Utilities

TypeScript’s type utilities come bundled into its standard library. Table B-1 enumerates all of the available utilities at the time of writing.

See es5.d.ts for an up-to-date reference.

Table B-1. Type utilities
Type utility	Use it on	Description
`ConstructorParameters`	Class constructor types	A tuple of a class constructor’s parameter types
`Exclude`	Union types	Exclude a type from another type
`Extract`	Union types	Select a subtype that’s assignable to another type
`InstanceType`	Class constructor types	The instance type you get from `new`-ing a class constructor
`NonNullable`	Nullable types	Exclude `null` and `undefined` from a type
`Parameters`	Function types	A tuple of a function’s parameter types
`Partial`	Object types	Make all properties in an object optional
`Pick`	Object types	A subtype of an object type, with a subset of its keys
`Readonly`	Array, Object, and Tuple types	Make all properties in an object read-only, or make an array or tuple read-only
`ReadonlyArray`	Any type	Make an immutable array of the given type
`Record`	Object types	A map from a key type to a value type
`Required`	Object types	Make all properties in an object required
`ReturnType`	Function types	A function’s return type

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