get.ts

const obj = {
    a: {
        b: {
            c: [1, 2, 3]
        },
        d: '',
        f: true,
    },
    g: {
        h: 2,
    },
    f: () => true,
    e: false,
}

type IsObject<T> = T extends (...args: any[]) => any
    ? false
    : T extends any[]
        ? false
        : T extends object
            ? true
            : false;

type IsArray<T> = T extends any[]
    ? true
    : false;

type ValueOfArray<T> = T extends (infer K)[]
    ? K
    : T

type DeepKeyOf<T extends ({ [K in any]: any } | any[])> = {
    [K in keyof T]: IsObject<T[K]> extends true
        ? Partial<[K, DeepKeyOf2<T[K]>]>
        : IsArray<T[K]> extends true
            ? Partial<[K, number[]]>
            : Partial<[K]>
}[keyof T];

type DeepKeyOf2<T extends ({ [K in any]: any } | any[])> = {
    [K in keyof T]: IsObject<T[K]> extends true
        ? Partial<[K, DeepKeyOf3<T[K]>]>
        : IsArray<T[K]> extends true
            ? Partial<[K, number[]]>
            : Partial<[K]>
}[keyof T];

type DeepKeyOf3<T extends ({ [K in any]: any } | any[])> = {
    [K in keyof T]: IsObject<T[K]> extends true
        ? Partial<[K, DeepKeyOf4<T[K]>]>
        : IsArray<T[K]> extends true
            ? Partial<[K, number[]]>
            : Partial<[K]>
}[keyof T];

type DeepKeyOf4<T extends ({ [K in any]: any } | any[])> = {
    [K in keyof T]: IsObject<T[K]> extends true
        ? Partial<[K, DeepKeyOf5<T[K]>]>
        : IsArray<T[K]> extends true
            ? Partial<[K, number[]]>
            : Partial<[K]>
}[keyof T];


type DeepKeyOf5<T> = {
    [K in keyof T]: Partial<IsArray<T[K]> extends true
        ? [K, number[]]
        : [K]>
}[keyof T];

const get = <T extends (any[] | {[K in number | string]: any}),
    K extends DeepKeyOf<T>,
    R = undefined>(
    objOrArr: T,
    keys: K,
    defaultValue?: R,
) => {
    return defaultValue;
}

// const res = get(obj, ['a', 'b', 'c', 2]); error
const c: DeepKeyOf<typeof obj> = ['a', ['b', ['c', [2]]]]