var only = require('only-nested')

var whitelist = {
  a: null,
  b: {
    x: null,
    y: null
  }
}

var obj = {
  a: 1,
  b: {
    x: 2,
    y: 3,
    z: 4
  },
  c: 5
}

only(whitelist, obj)
/*
-> {
  a: 1,
  b: {
    x: 2,
    y: 3
  }
}
*/

var whitelistWithArray = {
  a: [{
    x: null
  }]
}

var objWithArray = {
  a: [
    {
      x: 1,
      y: 2
    },
    {
      x: 3,
      y: 4,
      z: 5
    }
  ]
}

only(whitelistWithArray, objWithArray)
/*
-> {
  a: [
    {
      x: 1
    },
    {
      x: 3
    }
  ]
}
*/

var onlyWhitelist = only(whitelist)
onlyWhitelist(obj)

someArrayOfObjects.map(only({a: null}))