Pull values from array to a new single array

I have an array like this:

pa: [{ 
  id: 1,
  sa: [ 1, 2, 3 ]
}, {
  id: 2,
  sa: [ 1, 2, 3 ]
}, {
  id: 3,
}]

Some of the objects contain an sa array and some don’t. I want to create a new array that contains all the numbers of sa in a new single array

I have tried this but it will add in multiple arrays

for (let i = 0; i < pa.length; i++) {
  if (pa[i].sa!== undefined && pa[i]?.sa) {
    f.push(p[i]?.sa?.map(a=> a.id));
  }
}

i want the final array to be

newArray = [1,2,3,1,2,3]

>Solution :

You could take a flat mapping with a destructuring with optional array.

const
    data = { pa: [{ id: 1, sa: [1, 2, 3] }, { id: 2, sa: [1, 2, 3] }, { id: 3 }] },
    result = data.pa.flatMap(({ sa = [] }) => sa);

console.log(result);