Flatten Object Functions

flatJSONreturnArr.js

// Export from your streaming service like Spotify, YT music, etc.
const artistsByGenre = {
    jazz: ['Miles Davis', 'John Coltrane'],
    rock: {
        classic: ['Bob Seger', 'The Eagles'],
        hair: ['Def Leppard', 'Whitesnake', 'Poison'],
        alt: {
            classic: ['Pearl Jam', 'The Killers'],
            current: ['Joywave', 'Sir Sly']
        }
    },
    unclassified: {
        new: ['Caamp', 'Neil Young'],
        classic: ['Seal', 'Morcheeba', 'Chris Stapleton']
    }
}

const getArtistNames = (dataObject, array = []) => {
    Object.keys(dataObject).forEach(key => {
        if (Array.isArray(dataObject[key])) {
            return dataObject[key]
            .forEach(artist => array.push(artist))
        }
        getArtistNames(dataObject[key], array)
    })
    return array
}

console.log(getArtistNames(artistsByGenre).join('\n'))

flatJSONreturnJSON.js

function flatObject(nestedObject, parentKey = '') {
    let flattenedObject = {}

    Object.entries(nestedObject).map(([key, value]) => {
        const newKey = parentKey ? parentKey + '_' + key : key 
        if (typeof value != 'object') return flattenedObject[newKey] = value

        const objectValueFlattened = flatObject(value, newKey)
        flattenedObject = { ...flattenedObject, ...objectValueFlattened}
    })
    
    return flattenedObject
}

Two versions: With former you will get an array as return, with latter you will get a json. Choose according to your logic needs.