ExtractField is a utility type that extracts the type of a specific field from a type T.
This type takes two parameters:
T, the type from which the field type is to be extracted.
K, the key of the field to be extracted from T.
The utility type works as follows:
T extends Record<K, infer U>: This conditional check verifies if T can be assigned to a
record type with a key K and some value. If it can, TypeScript infers the type of this value
and assigns it to U.
U is returned when T is assignable to Record<K, infer U>, i.e., when T has the key K.
If T does not have the key K, the utility type returns never.
This utility type is powerful as it allows the extraction of a specific field's type
dynamically, given the field's name. It is useful when working with complex and dynamic types
where the structure might not be known ahead of time.
ExtractField is a utility type that extracts the type of a specific field from a type
T. This type takes two parameters:T, the type from which the field type is to be extracted.K, the key of the field to be extracted fromT.The utility type works as follows:
T extends Record<K, infer U>: This conditional check verifies ifTcan be assigned to a record type with a keyKand some value. If it can, TypeScript infers the type of this value and assigns it toU.Uis returned whenTis assignable toRecord<K, infer U>, i.e., whenThas the keyK.If
Tdoes not have the keyK, the utility type returnsnever.This utility type is powerful as it allows the extraction of a specific field's type dynamically, given the field's name. It is useful when working with complex and dynamic types where the structure might not be known ahead of time.