Comparing 2 array values push only first result

Question

I have an array which i need to compare it's values - and if there are duplication - i want to store them in array, for example :

 obj1 = [{"manager_id":1,"name":"john"},{"manager_id":1,"name":"kile"},
 {"manager_id":2,"name":"kenny"},
 {"manager_id":4,"name":"stan"}]

 obj2 = [{"employees_id":1,"name":"dan"},
 {"employees_id":1,"name":"ben"},{"employees_id":1,"name":"sarah"},
 {"employees_id":2,"name":"kelly"}]

If "manger_id" === "employees_id - then the result would be :

 // {1:[{"manager_id":1,"name":"john"},{"manager_id":1,"name":"kile"},
    {"employees_id":1,"name":"dan"}, {"employees_id":1,"name":"ben"},
    {"employees_id":1,"name":"sarah"}]};

I've tried :

var obj1 = [{
  "manager_id": 1,
  "name": "john"
}, {
  "manager_id": 1,
  "name": "kile"
}, {
  "manager_id": 2,
  "name": "kenny"
}, {
  "manager_id": 4,
  "name": "stan"
}];

var obj2 = [{
  "employees_id": 1,
  "name": "dan"
}, {
  "employees_id": 1,
  "name": "ben"
}, {
  "employees_id": 1,
  "name": "sarah"
}, {
  "employees_id": 2,
  "name": "kelly"
}];

var res = obj1.concat(obj2).reduce(function(r, o) {

  r[o.manager_id] = r[o.employees_id] || [];
  r[o.manager_id].push(o);


  return r;
}, {});


console.log(res);

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As you can the results of the "manager_id" aren't added - only one - when there should be more

if manager_id === employees_id // should output in the first key

{1:[{"manager_id":1,"name":"john"},{"manager_id":1,"name":"kile"},
    {"employees_id":1,"name":"dan"}, {"employees_id":1,"name":"ben"},
    {"employees_id":1,"name":"sarah"}]}; 

As you can see there are several common id's

Answer 1

r[o.manager_id] = r[o.employees_id] || []; in this statement if a manager didn't have an employee_id the array was being reset for that id.

One way doing it right is this:

var res = obj1.concat(obj2).reduce(function(r, o) {
  var id;
  if(o.hasOwnProperty('manager_id')) {
    id = o['manager_id'];
  }
  else {
    id = o['employees_id'];
  }

  r[id] = r[id] || [];
  r[id].push(o);

  return r;
}, {});