If I have a type like: type T = { a: string, _a: string, b: number, _c: boolean, /* … any number of unknown properties … */ }; Is there anyway I can define a new mapped type which has all (and only) properties of T which do not begin with the letter _? For… Read More Typescript mapped type with filtered keys

I’m trying to figure out how to use Mapped Types with React UseState import * as React from ‘react’; import logo from ‘./logo.svg’; import ‘./App.css’; function App() { type MapType = { [id: number]: string[]; }; let id_sab: number = 1; let sab: string[] = ["a", "b"] let scde: string[] = ["c", "d", "e"]; let… Read More How to use Mapped Types with React.useState?

The use case is as follows I have got type A = { a: number | undefined b: string } // I want a helper type that will make so that the result is type B = { a: number| null b: string } type A = { a: number | null b: string }… Read More Typescript replace null with undefined type

Supposed I have the following interface: interface Person { name: string; age: number; location: string; } I want to extend it to have 3 additional properties, one for each of the interfaces’ original properties. So final outcome I want is: interface Person { name: string; nameHidden: boolean; age: number; ageHidden: boolean; location: string; locationHidden: boolean;… Read More Extend an interface with new set of properties based on original interface with mapped types

I have a createDispatcher function that accepts a record of functions. It will return a dispatch function that expects a record with a key corresponding to a key in the record fed to createDispatcher before. Kinda hard to explain, but have look at the examples below, I think it should become obvious. const funcs =… Read More strongly typed dispatcher function

If I have… type TypeNonGeneric = { prop1: any, prop2: string }; How can I map this to… type TypeGeneric<T> = { prop1: T, prop2: string }; I’ve looked at the docs and it seems that it needs to be a new generic type that would take TypeNonGeneric as a parameter, iterate over its keys… Read More Map property of type any/unknown to generic type T

Working purely on a type level. Given the following scenario: type Command<Type extends string> = { type: Type }; type Handler<Type extends string, Dependencies> = (cmd: Command<Type>, deps: Dependencies) => void; type CommandA = Command<"A">; type CommandB = Command<"B">; type MockServiceA = { foo: () => boolean }; type MockServiceB = { bar: () =>… Read More "Where clause" in mapped type

Is there a way to automatically generate a type based on a dictionary value? E.g. given this dictionary of constant values: export const SHIPMETHODS: OptionsMap<UpsShipMethodOption> = { ‘UPS’: ‘GND’, ‘UPS AIR2’: ‘2DA’, ‘UPS 3DAY SELECT’: ‘3DS’ } Is there a way to automatically generate a type like this, without having to duplicate everything? export type… Read More How to create a Typescript type based on the keys/values of a dictionary?

I’m trying to create a type based on a design token JSON file. The JSON object has the following format: { "Black": { "4": { "value": "#f6f6f6" }, "6": { "value": "#f2f2f2" }, "10": { "value": "#e8e8e8" }, "20": { "value": "#d3d3d3" }, "30": { "value": "#bcbcbc" }, "40": { "value": "#a7a7a7" }, "50": {… Read More How to create mapped union type from nested object from object keys

I’d like to reverse the property names and types for a record that has unique constant property values. const VALUE = { field1: "fieldA", field2: "fieldB" } as const type Reversed = Reverser<typeof VALUE> //which should yield the following type type Reversed = { fieldA: "field1"; fieldB: "field2"; } I dont think it is possible… Read More Record Type Reverser