I wonder how to make this getter more type-safe: VALUES = { '1': 'One', '2': 'Two', '3': 'Three' } def get(key : str) -> str: return VALUES[key] Instead of the type str I would love to ha...

I am working with Typescript and firebase and I have a small abstraction layer with this function to search for a unique document base on its field name and its value. where<K extends keyof (T ...

I've been trying to create a type that consists of the keys of type T whose values are strings. In pseudocode it would be keyof T where T[P] is a string. The only way I can think of doing this is ...

I'd like to be distinguish the following function types in conditional type checks: type SyncFn = () => void; type AsyncFn = (data: number) => Promise<void>; type SyncFnWithArg = (data:...

I would like to declare a type-enforced array of items and be able to derive a union type from it. This pattern works if you do not explicitly give a type to the items in the array. I am not sure h...

So from: export interface Category{ val: string; icon: string } const categoryArray: Category[] = [ { val: 'business', icon: 'store' }, { val: 'media', icon: 'video' }, { val: 'people',...

Is there a way to make the following type check? function getNumberFromObject<T>(obj: T, key: keyof T): number { return obj[key] // ERROR: obj[key] might not be a number } I want to speci...

I have a simple Typescript function like this: function getProperty<T, K extends keyof T>(obj: T, key: K): number { return obj[key]; // This line is not compiling. // Typescript will yell:...

Explain to me what keyof typeof means in TypeScript Example: enum ColorsEnum { white = '#ffffff', black = '#000000', } type Colors = keyof typeof ColorsEnum; The last row is equivalent to: type...

Let's say we have TypeScript code that looks like: type User = { id: number, name: string, } let user1: User = {id: 123, name: "Hello"}; let user2: User = {id: 456, name: "World"}; let keys: (...

Apologies, I'm sure this has been answered somewhere, but I'm not sure what to google. Please do edit my question if the terms in the title are wrong. I have something like this: type RowData = Rec...

In TypeScript, some types are defined using extends keyof or in keyof. I have tried to understand what they mean, but so far I didn't succeed. What I got is that keyof alone returns a union type wh...

I need to use some subset of class properties names as values in a map to use inside of the class. In following example I've replaced map by array. The problem is that if property is marked private...

I want to have a method that accepts an array of objects and an array of some of the objects keys. The method will return an array of arrays of object values but only of the selected keys. data: ...

I wondering how to correctly infer 2th and 3th template of my function suppose a simple interface interface ISome { a: string; b?: { c: string; }; } The following works: function pathBuilder&l...

In one file I have something like this: export const _all = { a: '', b: '', c: '', d: '', e: '', f: '', } type AllKeysType = typeof _all; export type AllKey = keyof AllKeysType; In another...

I would like to declare a type that requires all the keys of a given type T to be included in an array, e.g.: checkKeys<T>(arr: Array<keyof T>): void { // do something } interface My...

I want to define an Array type that must contain a chain of nested property names of a given type. Let's say I have a type: type Foo = { outer: { inner: any; } } Now I want to define an Ar...

I try to write a generic function which assembles update data for database updates. Passed arguments: record to be updated property key a new array item Even though I restrict the key's type u...