如何从 object (JavaScript) 中的数组中获取数据

Question

I'm trying get data from array so that look like this:

[Rome, Milan, Barselona, Madrid]

and my brain seems like go to blackout... How can i do this?

const countries = {
        italy: {
            id: 1,
            cities: ["Rome", "Milan"],
        },
        spain: {
            id: 2,
            cities: ["Barselona", "Madrid"],
        }
    };

    function getCitiesDates(data) {
    
    }

Answer 1

Using Object#values and Array#flatMap :

 function getCitiesDates(data) { return Object.values(data).flatMap(({ cities = [] }) => cities); } const countries = { italy: { id: 1, cities: ["Rome", "Milan"] }, spain: { id: 2, cities: ["Barselona", "Madrid"] } }; console.log( getCitiesDates(countries) );

Answer 2

You can get it in one line with Object.keys(data).flatMap(c => data[c].cities);

 const countries = { italy: { id: 1, cities: ["Rome", "Milan"], }, spain: { id: 2, cities: ["Barselona", "Madrid"], } }; function getCitiesDates(data) { return Object.keys(data).flatMap(c => data[c].cities); } console.log(getCitiesDates(countries))

Answer 3

One way to solve it could be to use Object.keys(), loop the Keys and then map the cities.

Something like this:

const keys = Object.Keys(countries);
const cities = keys.flatMap(key => conutries[key].cities)

console.log(cities) // [Rome, Milan, Barselona, Madrid]