基于计数添加索引合并两个javascripts数组对象

var arr1 = [{id: 1, name: 'John'}, {id: 2, name: 'Jane'}];
var arr2 = [{id: 3, name: 'Bob'}, {id: 4, name: 'Alice'}];

var mergedArray = arr1.concat(arr2);

var indexMap = {};

mergedArray.forEach(function(element) {
  if (indexMap[element.id]) {
    indexMap[element.id].count++;
  } else {
    indexMap[element.id] = {
      index: mergedArray.indexOf(element),
      count: 1
    };
  }
});

var resultArray = Object.keys(indexMap).map(function(key) {
  return {
    id: parseInt(key),
    index: indexMap[key].index,
    count: indexMap[key].count
  };
}).sort(function(a, b) {
  return a.index - b.index;
});