Create a nested Object from simple Array

Question

I'm trying to create a deep nested JS Object out of a simple array. The tricky part is that the next item in the array should always be added to the previous one.

Assuming my array looks like this:

const filters = [
 [
 {brand: {eq: 'BMW'}},
 {brand: {eq: 'AUDI'}}
 ],
 [
 {year: {eq: '2019'}},
 {year: {eq: '2020'}}
 ],
 [
 {country: {eq: 'CH'}},
 {country: {eq: 'DE'}}
 ]
]

How can I get a Object with that structure?

 query: {
 and: {
 or: [
 { brand: { eq: 'BMW' } },
 { brand: { eq: 'AUDI' } }
 ],
 and: {
 or: [
 { year: { eq: '2019' } },
 { year: { eq: '2020' } }
 ],
 and: {
 or: [
 { country: { eq: 'CH' } },
 { country: { eq: 'DE' } }
 ],
 ... and so on
 }
 }
 }
 },

How do I achieve to add a new "or" block to the previous "or" block?

Answer 1

You can build up a nested structure as you go through the array. For each item, add a nested object with an or key that links to the item and each following iteration work on the previous item

const filters = [
 [
 {brand: {eq: 'BMW'}},
 {brand: {eq: 'AUDI'}}
 ],
 [
 {year: {eq: '2019'}},
 {year: {eq: '2020'}}
 ],
 [
 {country: {eq: 'CH'}},
 {country: {eq: 'DE'}}
 ]
]
const query = {};
let current = query;
for (const filter of filters) {
 current.and = { or: filter };
 current = current.and; 
}
console.log(query);

• sp00m: Sometimes, nothing beats a good ol' for loop.
• VLAZ: For the record, the reduce version isn't horrible but I find it quite unnecessary: query = {}; filters.reduce((current, filter) => { current.and = { or: filter }; return current.and}, query)
• VLAZ: @sp00m I'm not really bothered by the hackyness. I'm mostly bothered that the reduce is basically a loop as the result is ignored. We can also shorten the for..of similarly: for (const or of filters) current = current.and = { or } Although, I guess the reduce can be golfed more.

Answer 2

Just for the reduce challenge:

const filters = [
 [
 {brand: {eq: 'BMW'}},
 {brand: {eq: 'AUDI'}}
 ],
 [
 {year: {eq: '2019'}},
 {year: {eq: '2020'}}
 ],
 [
 {country: {eq: 'CH'}},
 {country: {eq: 'DE'}}
 ]
];
const query = {};
filters.reduce((x, or) => x.and = { or }, query);
console.log(query);

Hacky as hell though:

• reduce with side-effects
• returns an assignment

VLAZ's approach is the way to go.

• VLAZ: Not recommended but at least it's fun. Just for the sake of completeness, there isn't a major downside to this other than readability. Returning the value from an assignment is probably the worst offender here but overall, it's not terrible.