function deepSum(o,n) {
  var c=0;
  _.each(_.keys(o||{}), k => { k===n ? c+=parseInt(o[n])||0 : c+=deepSum(o[k],n)});
  return c;
}

var item = {
  doc_count: 2,
  val: {
    buckets: [{
      one: {
        doc_count: 10,
        count: 100
      },
      two: {
        doc_count: 2
      }
    }, {
      doc_count: 3
    }],
    doc_count: 4
  }
}

var total = deepSum(item, "doc_count");
console.log("Total 21 === ", total);

var fail_path_item = {
  doc_count: null,
  val: {
    buckets: [{
      one: {
        doc_count: [],
        count: 100,
        test: {
          doc_count: function(){ return 1000 }
        }
      },
      two: {
        doc_count: "",
        nested: {
          doc_count: 5
        }
      }
    }, {
      doc_count: "zxc0FF"
    }],
    doc_count: 7,
    undef:{
      doc_count: undefined
    }
  }
}

console.log("Total 12 === ", deepSum(fail_path_item, "doc_count"));
console.log("Total 15 === ", deepSum({doc_count: "0xF"}, "doc_count"));
console.log("Total 0 === ", deepSum({}, "doc_count"));
console.log("Total 0 === ", deepSum(null, "doc_count"));
console.log("Total 0 === ", deepSum(undefined, "doc_count"));
console.log("Total 0 === ", deepSum(NaN, "doc_count"));
console.log("Total 0 === ", deepSum(1/0, "doc_count"));

function Obj(){
  this.doc_count = 1
}
Obj.prototype.createNested = function() {
  this.prop = {
    doc_count: 10
  }
}
var objItem = new Obj()
objItem.createNested()
console.log("Total 11 === ", deepSum( objItem, "doc_count"));


class User {
  constructor( count ) {
    this.score = count ;
    this.prevScores = [{ score: count+1 }]
  }
}
console.log("Total 201 === ", deepSum( new User(100), "score"));