A function that updates JSON disk object

So I have created this function that will add a disk if needed and it takes a disk and a size as inputs. The idea is that I need to update data.disks with a few properties. Disk is called from an external request and it follows the pattern of “disk1”, “disk2” and so on. Looking at it there are a few hard-coded values and some that are null. However I left them on purpose to show the structure of data.disk for the next person that might read it or modify it. Because of this it looks verbose and I don’t really like it all that much.
Do you see a way to make this function more readable/better in any way?

function addDisk(disk, size) {
    var diskNumber = disk.slice(-1);
    var diskLabel = "Hard disk " + diskNumber;
    var diskIndex = diskNumber - 1;

    //Updating JSON data object
    data.disks[diskIndex] = {
        "componentTypeId" : "com.vmware.csp.iaas.blueprint.service",
        "componentId" : null,
        "classId" : "Infrastructure.Compute.Machine.MachineDisk",
        "typeFilter" : null,
        "data" : {
            "capacity" : size,
            "custom_properties" : null,
            "id" : null,
            "initial_location" : "",
            "is_clone" : false,
            "label" : diskLabel,
            "storage_reservation_policy" : "",
            "userCreated" : true,
            "volumeId" : diskIndex
        }
    }
    log(diskLabel + " has capacity of: " + size + " GBs");
}

You could define a default disk object, so you can show all fields on default values and document the values allowed for each:

var DiskSkelethon = {
    "componentTypeId" : "com.vmware.csp.iaas.blueprint.service",
    "componentId" : null,
    "classId" : "Infrastructure.Compute.Machine.MachineDisk",
    "typeFilter" : null,
    "data" : {
        "capacity" : -1,
        "custom_properties" : null,
        "id" : null,
        "initial_location" : "",
        "is_clone" : false,
        "label" : "",
        "storage_reservation_policy" : "",
        "userCreated" : true,
        "volumeId" : -1
    }
}

Then in your function you will make a copy of it and override just the fields you’re changing:

function addDisk(disk, size) {
    var diskNumber = parseInt(disk.slice(-1), 10);
    if (isNaN(diskNumber)) {
       log("some error...");
       return false;
    }
    var diskLabel = "Hard disk " + diskNumber;
    var diskIndex = diskNumber - 1;

    //Updating JSON data object
    var diskData = Object.assign({}, DiskSkelethon)

    diskData.data.capacity = size;
    diskData.data.label = diskLabel;
    diskData.data.volumeId = diskIndex

    data.disks[diskIndex] = diskData
    log(diskLabel + " has capacity of: " + size + " GBs");
}

I think this code is fine, if you use it professionally I would

• Document that size must be provided in Gigs
• Verify that size actually is a number, or can be parsed as a number, throw an exception otherwise
• Document how the parameter disk must be formatted

• Verify that disk.slice(-1) is a number, or can be parsed as a number, throw an exception otherwise

• Note that data.disks seems a global variable, personally, I would have prefered to see a setter function for updating a disk object.