normalized.js

state = { peopleIds: [], people: {}, hobbies: {} }

people = [
    {
        id: 1,
        name: 'Person 1',
        hobbies: [
            {
                id: 11,
                name: "Dark Souls",
                type: "SinglePlayer"
            },
            {
                id: 22,
                name: "Call of Duty",
                type: "Multiplayer"
            }
        ]
    },
    {
        id: 2,
        name: 'Person 2',
        hobbies: [
            {
                id: 11,
                name: "Dark Souls",
                type: "SinglePlayer"
            },
            {
                id: 33,
                name: "God of War",
                type: "SinglePlayer"
            }
        ]
    }
]


people.map( person => {
    state.peopleIds = [
        ...state.peopleIds,
        person.id
    ]

    hobbies = [...person.hobbies]

    state.people[person.id] = { 
        ...person, 
        hobbies: hobbies.map( h => h.id )
    }

    hobbies.map( hobby => {
        state.hobbies[hobby.id] = { ...hobby }
    })
})


console.dir(state, { depth: null });