so I have this collection:

I am trying to only get the groupID's in the array there are like 3 of them, but I tried a for loop in a for loop but it keeps returning undefined. Where am I going wrong?

fire.firestore().collection('userEvents2').doc(fire.auth().currentUser.uid).set({
    groups: groupsList
})


for (let i = 0; i < groupsList.length; i++) {
    const key = "";
    for (key in groupsList[i]) {
        console.log(key.groupID)
      }
    
  }