ts-pathof

Typesafe path to variable
Implementation of https://github.com/Microsoft/TypeScript/issues/20423

There is limitations for 2 level deep with type hacks, so no infinit tuples

Install & Use

npm i ts-pathof --save-exact

import { pathOf } from 'ts-pathof';

const c = { z: { y: { bb: 123 }}};
const path = pathOf(c, 'z', 'y', 'bb');

// path now is typeof [ 'z', 'y', 'bb' ]
const path2 = pathOf(c, 'z', 'y', 'gg'); // error, because no 'gg' field in c.z.y

Maximum 10 levels deep limitation on pathOf

Path as tuple

import { hasPath } from 'ts-pathof';

const c = { z: { y: { bb: 123 }}};
const path = hasPath(c, [ 'z', 'y', 'bb' ]); // ok
const path2 = hasPath(c, [ 'z', 'y', 'gg' ]); // false & compilation error

Maximum 20 levels deep limitation on hasPath

Type only assertion

Use pathOfN (where N is deep), to pick tuple-type path to field
Maximum 10 levels deep

Eg:

let path: pathOf3<typeof c, 'z', 'y', 'bb'>;
path = pathOf(c, 'z', 'y', 'bb');

Use other type-only variant (with 20 levels limitation on deep), PathOf:

const o = {x: { y: 10 }};

type xy = PathOf<typeof o, ['x', 'y']>; // ok

type xyz = PathOf<typeof o, ['x', 'y', 'z']>; // error

PS

Check out typedpark, and Variadic Kinds thread for more info on advenced tuple utils.
Eg picking head or tail of tuple, reverse or join.

type composed = Compose<[boolean, string], [number]>;

composed -> [boolean, string, number]

Also checkout tsargs, utility types for arguments.