javascript - Split promise variable into named variables -

i have this

promise.all(   categories.map(category => collection.find({ category })) ).then(items => {   return items }) 

but array same length categories each element array of items found in collection within specific category.

what want return object keys categories.

so if categories football, volleyball, , motorsport, want

{   'football': [...],   'volleyball': [...],   'motorsport': [...] } 

instead of

[   [...],   [...],   [...] ] 

as have now.

if number of categories static, guess this

promise.all(   categories.map(category => collection.find({ category })) ).then(([football, volleyball, motorsport]) => {   return {     football,     volleyball,     motorsport   } }) 

since items array has similar order of categories array, can use array#reduce combine them object using item, , category label of same index:

promise.all(   categories.map(category => collection.find({ category })) ).then(items => {   return items.reduce((o, item, i) => {     o[categories[i]] = item;      return o;   }, {}); }) 

and since using es6, might want create map instead:

promise.all(   categories.map(category => collection.find({ category })) ).then(items => {   return items.reduce((map, item, i) => map.set(categories[i], item), new map()); })