Read object within array in nodejs

Question

I am trying to get the _id from the objects within an array.

[ { _id: 5ba49c6304daff5034e6fa6a,
    email: '[email protected]',
    active: true,
    events: [ [Object], [Object], [Object] ],
    name: { first: 'editor', last: 'editor' } } ]

Each object within events array contains a _id. I need to get those ids in another array.

if (userobj.events) {
   if (userobj.events[0]) {
         var eIds = [];
         for (var i = 0; i<userobj.events.length; i++) {
             console.log(userobj.events._id);
             eIds.push(userobj.events._id);
         }
             andArr.push({"_id":{"$in":eIds}});
      }
  }

I am getting undefined for each _id.

Any help is highly appreciated.

Does your events property objects contain _id property? If it contains just use for (var i = 0; i < userobj.events.length; i++) { console.log(userobj.events[i]._id); } — Isabek Tashiev
– Isabek Tashiev, Commented Sep 21, 2018 at 15:50

Mohammed Ashfaq · Accepted Answer · 2018-09-21 16:14:59Z

2

userobj ={ 
  _id: '5ba',
  email: '[email protected]',
  active: true,
  events: [ {_id:23},{_id:34},{_id:56},{}],
}

let listOfId = [];
userobj.events.map(({_id})=> { if(_id) listOfId.push(_id) });
console.log("listOfId",listOfId);

edited Sep 21, 2018 at 16:14

answered Sep 21, 2018 at 16:00

Mohammed Ashfaq

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Comments

DedaDev · Accepted Answer · 2018-09-21 16:04:23Z

2

You are missing the [i] after events and before ._id in for loop.

userobj.events[i]._id

This is whole your code in one line:

let eIds = userobj.events.map(ele=>ele._id)

edited Sep 21, 2018 at 16:04

answered Sep 21, 2018 at 15:55

DedaDev

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Comments

Isabek Tashiev · Accepted Answer · 2018-09-21 16:51:59Z

2

I would like to improve your solution. First, you are checking for null. Then you are pushing ids to the array. Here you can use some JS tricks and arrow functions like this;

let obj = { events: [ {_id: 1}, {_id: 2}, {_id: 3}] };

let eventIds = (obj.events || []).map(event => event._id);

console.log(eventIds);

Also, you can use ES6 destructuring as Muhammad shows;

let eventIds = (obj.events || []).map(({_id}) => _id);

Btw you can use reduce like this.

let eventIds = (obj.events || []).reduce((acc, elem) => {
    if(elem._id) {
       acc.push(elem._id);
    }
    return acc;
}, []);

edited Sep 21, 2018 at 16:51

answered Sep 21, 2018 at 16:01

Isabek Tashiev

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