input.js

alternative_output.js

{
    "_id": "123",
    "members": [
        {
            "_id": "789" 
        } 
    ]
}

gistfile1.js

{
    "_id": "123",
    "title": "whatever",
    "members": [
        {
            "_id": "456",
            "name": "John",
            "active": true 
        },
        {
            "_id": "789",
            "name": "Bob",
            "active": false 
        } 
    ]
}

output.js

{
    "_id": "123",
    "title": "whatever",
    "members": [
        {
            "_id": "789",
            "name": "Bob",
            "active": false 
        } 
    ]
}