I have a third-party library which extend Sting prototype with new method: String.prototyp.someMethod = () => null; This library should be imported as side-effect library import ‘target-library’ I am trying to write declaration file for this module, but keeping clean the global types from this string extension. For instance, if I do like this //… Read More Extend global type inside module declaration

I have the following object with a const assertion: const foo = { bar: [‘a’, ‘b’], } as const; My goal is to write a function that updates the bar array and correctly infers the new type. I can achieve the intended result when I pass foo.bar into the function: type Bar = Readonly<string[]>; function… Read More TypeScript const assertion: Avoid type widening inside function

I am working with the following types: type Fruits = { type: ‘banana’ | ‘peach’ | ‘kiwi’, price: null | string; } type FruitsWithNonNull = Pick<Fruits, ‘type’> & { price: NonNullable<Fruits[‘price’]> } const fruits:Fruits[] = [{type:’banana’, price:null}, {type:’peach’, price:null},{type:’peach’, price:’12’}] const filteredFruits:FruitsWithNonNull[] = fruits.filter(fruit => fruit.price !== null); I get this error from filteredFruits: Type… Read More How to convince TypesSript you will return an Array with a property that is not null

I have an array and I want to get a type which constrains its possible values to just valid keys. I thought that keyof typeof array would solve this, but it accepts all numbers. const arr = ["a", "b", "c"] as const type keyOfArr = keyof typeof arr // Does not work work. Accepts all… Read More Constrain type to keys of array but respect length