strictnullchecks - w3toppers.com

Why does TypeScript infer the ‘never’ type when reducing an Array with concat?

I believe this is because the type for [] is inferred to be never[], which is the type for an array that MUST be empty. You can use a type cast to address this: [‘a’, ‘b’, ‘c’].reduce((accumulator, value) => accumulator.concat(value), [] as string[]); Normally this wouldn’t be much of a problem since TypeScript does a … Read more

Typescript and filter Boolean

You can use functions like this function nonNullable<T>(value: T): value is NonNullable<T> { return value !== null && value !== undefined; } type Truthy<T> = T extends false | ” | 0 | null | undefined ? never : T; // from lodash function truthy<T>(value: T): value is Truthy<T> { return !!value; } [1, 2, … Read more