How to the get the sum of all the field with the same name in a nested array?

I’m trying to find the sum of all the field values of the nested array, I suck at explaining stuffs like this, I hope the code below will give you some insight of what I want to do.

The array looks like this

data = [
    {
        id: 8434,
        name: listName, 
        data: [
            {name: "a name",
             quantity: 20,
            }
            {name: "another name",
             quantity: 40,
            }
            {name: "another new name",
             quantity: 40,
            }
        ]
    }, 
    {
        id: 54343,
        name: "new list name", 
        data: [
            {name: "a name",
             quantity: 12,
            }
            {name: "another name",
             quantity: 10,
            }
            {name: "another new name",
             quantity: 16,
            }
        ]
    }
]

This is how I want the data to be after carrying out the sum

transformed = [
{name: "a name", quantity: 32},
{name: "another name", quantity: 50},
{name: "another new name", quantity: 56}
]

>Solution :

just loop them through and create a new object..

const data = [
    {
        id: 8434,
        name: 'listName', 
        data: [
            {
                name: "a name",
                quantity: 20,
            },
            {
                name: "another name",
                quantity: 40,
            },
            {
                name: "another new name",
                quantity: 40,
            }
        ]
    }, 
    {
        id: 54343,
        name: "new list name", 
        data: [
            {
                name: "a name",
                quantity: 12,
            },
            {
                name: "another name",
                quantity: 10,
            },
            {
                name: "another new name",
                quantity: 16,
            }
        ]
    }
]


// Logic:
const transformed = []

data.forEach(d => {
    d.data.forEach(item => {
        const exist = transformed.find(t => t.name == item.name)
        if(exist) 
            exist.quantity += item.quantity
        else 
            transformed.push(item)
    })
})

console.log(transformed)

Output:

[
  { name: 'a name', quantity: 32 },
  { name: 'another name', quantity: 50 },
  { name: 'another new name', quantity: 56 }
]