node.js - Fetching fields which have values as array in mongodb -

my collection looks this

{a:"foo", b:[10,20,30]} {a:"boo", b:[15,25,35]} {a:"abc", b:[10,40,50]} {a:"xyz", b:[10,60,70]} 

now, want retrieve entire array under a:"foo". how do this?

db.collection.find({"a":"foo"}) 

will return object matching criteria , can access "b" element of results