How to loop over nested objects and arrays Javascript?

Question

I have an object which consists of keys and values as lists

myObj = { "key1": [{"value": 1, "date": "2020"}], [{"value": 2, "date": "2020"}],
 "key2": [{"value": 3, "date": "2020"}], [{"value": 4, "date": "2020"}]
 }

I need to get the value of "value" key in this nested objects and reassign it as an array to the key.

So my ideal result is

myObj = { "key1": [1,2],
 "key2": [3,4]
 }

What I did

So I tried to loop over the object

for (var [k, v] of Object.entries(myObj)) {
 v.forEach(function convertJSON(arr) {
 console.log(arr.value);
 });
 console.log(k, v);
 }

It works,

1
2
"key1": [{"value": 1, "date": "2020"}], [{"value": 2, "date": "2020"}]
3
4
"key2": [{"value": 3, "date": "2020"}], [{"value": 4, "date": "2020"}]

but when I tried to reassign the value it gives me undefined

for (var [k, v] of Object.entries(myObj)) {
 newValue = v.forEach(function convertJSON(arr) {
 console.log(arr.value);
 });
 v = newValue;
 console.log(k, v);
 }

UPDATE - Add my data

enter image description here

so I think it should like this

myData = { "impressions": [{value: 559, end_time: "2020年08月31日T07:00:00+0000"}], 
 [{value: 519, end_time: "2020年09月01日T07:00:00+0000"}],
 "reach": [{value: 334, end_time: "2020年08月31日T07:00:00+0000"}],
 [{value: 398, end_time: "2020年09月01日T07:00:00+0000"}}
}

Answer 1

You could take a flat map of the nested objects.

const
 object = { key1: [{ value: 1, date: "2020" }, { value: 2, date: "2020" }], key2: [{ value: 3, date: "2020" }, { value: 4, date: "2020" }] },
 result = Object.fromEntries(Object
 .entries(object)
 .map(([k, v]) => [k, v.map(({ value }) => value)])
 );
 
console.log(result);

• Anna: Cool, but unfortunately for me it returns Uncaught TypeError: a.map is not a funct

Answer 2

You can use Array.prototype.reduce() method to achieve your desired output. The syntax of array reduce array.reduce(function(total, currentValue, currentIndex, arr), initialValue). First get all the keys using Object.keys() method and then traverse it and map each item of that keyed object by using Array.prototype.map() method.

const myObj = {
 impressions: [
 { value: 559, end_time: '2020-08-31T07:00:00+0000' },
 { value: 519, end_time: '2020-09-01T07:00:00+0000' },
 ],
 reach: [
 { value: 334, end_time: '2020-08-31T07:00:00+0000' },
 { value: 398, end_time: '2020-09-01T07:00:00+0000' },
 ],
};
const ret = Object.keys(myObj).reduce((prev, c) => {
 const p = prev;
 p[c] = myObj[c].map((x) => x.value);
 return p;
}, {});
console.log(ret);