Merge Two json arrays whilst updating their content

Question

var Schedulearray1 = 
[{
    "scheduleid": "id123",
    "timestart": "08:00",
    "timeend": "20:00",
},
{
    "scheduleid": "id456",
    "timestart": "08:00",
    "timeend": "20:00",
}]

var Schedulearray2 = 
[{
    "scheduleid": "id123",
    "timestart": "08:00",
    "timeend": "20:00",
},
{
    "scheduleid": "id789",
    "timestart": "08:00",
    "timeend": "20:00",
}]

i want to merge these two json arrays i used :

Schedulearray1 = Schedulearray1.concat(Schedulearray2);

but this results in having 2 id123 for the schedule like follow

[{
    "scheduleid": "id123",
    "timestart": "08:00",
    "timeend": "20:00",
},
{
    "scheduleid": "id456",
    "timestart": "08:00",
    "timeend": "20:00",
},
{
    "scheduleid": "id123",
    "timestart": "08:00",
    "timeend": "20:00",
},
{
    "scheduleid": "id789",
    "timestart": "08:00",
    "timeend": "20:00",
}]

i want it to update the scheduleid timestart and timeend in Schedulearray2 by the ones available in Schedulearray1.

I have tried this from the similar question that you suggested:

 var mergedList = _.map(Schedulearray1, function(item) {
   return _.extend(item, _.findWhere(Schedulearray2, { scheduleid: item.id }));
 });

it resulted in an error Uncaught ReferenceError: _ is not defined