Collection of useful Typescript types

types.ts

declare global {
	interface ObjectConstructor {
		keys<O extends object>(o: O): (keyof O & string)[];
	}
}

/**
 * Returns tuple types that include every string in union
 * TupleUnion<keyof { bar: string; leet: number }>; 
 * ["bar", "leet"] | ["leet", "bar"];
 */
type TupleUnion<U extends string, R extends string[] = []> = {
	[S in U]: Exclude<U, S> extends never ? [...R, S] : TupleUnion<Exclude<U, S>, [...R, S]>;
}[U] & string[];
		
/**
 * Inline type predicate (removed by bundler)
 * if (foo.nodeType === 1 && Narrow<Element>(foo)) { /* forces <typeof foo> to be <Element> in this block */ }
 */
const Narrow = <T>(v): v is T => true;