Typescript Generic with Constraints

gistfile1.ts

interface INestable<T> {
    nestedList?: T[];
}

interface Item extends INestable<Item> {
    id: number;
    nestedList?: Item[];
}

const recursiveStructure: Item[] = [
    {
        id: 1,
        nestedList: [
            {
                id: 11,
            },
            {
                id: 22,
                nestedList: [
                    {
                        id: 33,
                    }
                ]
            }
        ]
    }
];

function forEachDeep<T extends INestable<T>>(array: T[], callback: (item: T) => void): void {
    array.forEach((elem: T) => {
        if (elem.nestedList) {
            forEachDeep(elem.nestedList, callback)
        }

        callback(item)
    })
}