Get Date from Nested Array of Objects and set that date as an Key in Node.js - node.js

Question

I'm using Node.js I have data like this:
const data= [
{"id":"1","date":"2022-09-07T15:56:32.279Z","req_id":"98"},
{"id":"2","date":"2022-09-08T15:48:19.075Z","req_id":"97"},
{"id":"3","date":"2022-09-06T15:48:19.073Z","req_id":"96"}
{"id":"4","date":"2022-09-06T15:48:19.073Z","req_id":"96"}
]
I want data in this format:
expected Output:
"2022-09-06":[
{"id":"4","date":"2022-09-06T15:48:19.073Z","req_id":"96"},
{"id":"3","date":"2022-09-06T15:48:19.073Z","req_id":"96"}
]
"2022-09-08":[
{"id":"2","date":"2022-09-08T15:48:19.075Z","req_id":"97"}
]
"2022-09-07":[
{"id":"1","date":"2022-09-07T15:56:32.279Z","req_id":"98"}
]

Answer 1

Assuming the dates are always in the same format, I would do something like this:
function mapData(data){
// returns the given date as an string in the "%dd-%mm-%yyyy" format
const getDateWithoutTime = (dateString) => dateString.split("T")[0];
const mappedData = [];
for(const req of data){
const formattedDate = getDateWithoutTime(req.date);
// if the key already exists in the array, we add a new item
if(mappedData[formattedDate]) mappedData[formattedDate].push(req);
// if the key doesn't exist, we create an array with that single item for that key
else mappedData[formattedDate] = [req];
}
return mappedData;
}

Answer 2

Straightforward solution using regex:
let result = new Map();
for (const item of data) {
let date = item['date'].match(/\d{4}-\d{2}-\d{2}/)[0];
let items = result.get(date) || [];
items.push(item);
result.set(date, items)
}