Edit: Since Typescript 4.1 there is a way of doing this directly with Key Remapping, avoiding the Pick combinator. Please see the answer by Oleg where it’s introduced. type RemoveIndex<T> = { [ K in keyof T as string extends K ? never : number extends K ? never : symbol extends K ? never … Read more
TS 4.1 You can use as clauses in mapped types to filter out properties in one go: type Methods<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] }; type A_Methods = Methods<A>; // { render: () => void; } When the type specified in an as clause resolves … Read more
With TS 2.8 and conditional types we can simply write: type DeepPartial<T> = { [P in keyof T]?: T[P] extends Array<infer U> ? Array<DeepPartial<U>> : T[P] extends ReadonlyArray<infer U> ? ReadonlyArray<DeepPartial<U>> : DeepPartial<T[P]> }; or with [] instead of Array<> that would be: type DeepPartial<T> = { [P in keyof T]?: T[P] extends (infer U)[] … Read more
The definition for Record is: /** * Construct a type with a set of properties K of type T */ type Record<K extends keyof any, T> = { [P in K]: T; }; When creating a type like type MyType = Record<string, string>;, inlining Record leads to the following type: type MyType = { [P … Read more
This can be done with conditional types and indexed access types, like this: type KeysMatching<T, V> = {[K in keyof T]-?: T[K] extends V ? K : never}[keyof T]; and then you pull out the keys whose properties match string like this: const key: KeysMatching<Thing, string> = ‘other’; // ERROR! // ‘”other”‘ is not assignable … Read more