件数と合計を求める

var data = [
  {name: 'Taro', score: 10},
  {name: 'Jiro', score: 20},
  {name: 'Mike', score: 30},
  {name: 'Mike', score: 40},
  {name: 'Mike', score: 50},
  {name: 'Mike', score: 60},
  {name: 'Mike', score: 70},
  {name: 'Mike', score: 80},
  {name: 'Mike', score: 90},
  {name: 'Mike', score: 100},
];

function countScore(data){
  var count = 0;
  var sum = 0;
  for(var i = 0; i < data.length; i++){
    var d = data[i];
    sum += d.score;
    count++;
  }
  return {
    count: count,
    sum: sum
  };
}

countScore(data);