Reduce & Nested Array

I am merging two arrays which is working great. But i am showing the data on a calendar and i need an array to be used as a single line.

My Data:

[
    {
        "pets": [
            {
                "name": "Hound",
                "id": "290dH8Z7nE3kKqMWcsj5"
            },

            {
                "name": "Roger",
                "id": "290dH8Z7nE3kKqMWcsj7"
            }
        ],
        "date": [
            {
                "date": "2023-05-11"
            }
        ],
        "typeofservice": "Service 1",
        "datestart": "2023-05-11",
        "outsideshift": false,
        "organizationId": "vrpMguv6cwf7L9KLEknR",
        "AddressLine1": "7j2UsMaCI1ehnHl5FbMf",
    }
]

   const partialDetails = a3.reduce((res, item) => {
  res.push({ Subject: item.typeofservice , StartTime: item.datestart, IsAllDay: true, CategoryColor: "#1aaa55", Description: "Address: " + item.AddressLine1 })
  return res;
}, []);

Results Currently

[
    {
        "Subject": "Service 1",
        "StartTime": "2023-05-11",
        "IsAllDay": true,
        "CategoryColor": "#1aaa55",
        "Description": "Address: AddressLine1Address"
    }
]

Wanted result the array in pets to be able to go into the subject line. There could be 1 there could be many.

[
    {
        "Subject": "Service 1 - Hound, Roger",
        "StartTime": "2023-05-11",
        "IsAllDay": true,
        "CategoryColor": "#1aaa55",
        "Description": "Address: AddressLine1Address"
    }
]

Ive tried map inside but that creates a new line

You can try:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const a = [
    {
        "pets": [
            {
                "name": "Hound",
                "id": "290dH8Z7nE3kKqMWcsj5"
            },

            {
                "name": "Roger",
                "id": "290dH8Z7nE3kKqMWcsj7"
            }
        ],
        "date": [
            {
                "date": "2023-05-11"
            }
        ],
        "typeofservice": "Service 1",
        "datestart": "2023-05-11",
        "outsideshift": false,
        "organizationId": "vrpMguv6cwf7L9KLEknR",
        "AddressLine1": "7j2UsMaCI1ehnHl5FbMf",
    }
]

 const partialDetails = a.reduce((res, item) => {
 const subject = item.typeofservice + ' - '+ item.pets.map(pet=>pet.name).join( ', ');
 
  res.push({ Subject: subject , StartTime: item.datestart, IsAllDay: true, CategoryColor: "#1aaa55", Description: "Address: " + item.AddressLine1 })
  return res;
}, []);

console.log(partialDetails)

<!-- end snippet -->

const partialDetails = data.reduce((res, item) => {
    res.push({ Subject: `${item.typeofservice} - ${item.pets.map((el)=>el.name).join(', ')}` , StartTime: item.datestart, IsAllDay: true, CategoryColor: "#1aaa55", Description: "Address: " + item.AddressLine1 })
    return res;
  }, []);

basically the same as previous answer using map and join for the names.