Inserting unique objects into array of objects using javascript?

Question

I am performing push operation to an array of objects. My code looks similar as shown below,

var obj = {"id":1, "fname":"john", "lname":"doe"};
var userArray = [{
   "id": 1,
   "fname": "john",
   "lname": "doe"
}, {
   "id": 2,
   "fname": "john",
   "lname": "doe"
}];

userArray.forEach(function (element) {
   if(element.id !== obj.id) {
      userArray.push(obj);
   }
});

console.log(userArray);

when i do push operation on userArray which already contains an object which i am pushing (from code it is var obj = {"id":1, "fname":"john", "lname":"doe"};) it pushes it to array on second pass in for loop.

Expected output should be userArray = [{"id": 1,"fname": "john","lname": "doe"}, {"id": 2, "fname": "john","lname": "doe"}];

but i am getting userArray = [{"id": 1,"fname": "john","lname": "doe"}, {"id": 2, "fname": "john","lname": "doe"}, {"id": 1,"fname": "john","lname": "doe"}];

How do i push only unique objects to array?

Change your if condition. Your condition should be to check for id if it fails for all the items in the array, then only add that object otherwise ignore it. — Hassan Imam
– Hassan Imam, Commented Jan 16, 2018 at 17:31
Add a flag before the loop and set its default value to false, inside the for loop, compare the id, if it matches set your flag value to true and break out of loop. Outside the loop, check the value of flag, and add object only if flag value is false. — Hassan Imam
– Hassan Imam, Commented Jan 16, 2018 at 17:37
If the array is modified during iteration, other elements might be skipped. — radarbob
– radarbob, Commented Jan 18, 2018 at 18:55

CRice · Accepted Answer · 2018-01-16 17:31:00Z

3

Use the array .some method to check if there is already an item in the list with that ID. If there isn't, then push into the array:

var obj = {"id":1, "fname":"john", "lname":"doe"};
var userArray = [{
   "id": 1,
   "fname": "john",
   "lname": "doe"
}, {
   "id": 2,
   "fname": "john",
   "lname": "doe"
}];

var existing = userArray.some(element => element.id === obj.id);
if(!existing) {
  userArray.push(obj);
}

console.log(userArray);

answered Jan 16, 2018 at 17:31

CRice

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Comments

Javier Gonzalez · Accepted Answer · 2018-01-16 17:33:16Z

1

You need to search for an user with the same id, if it does not exist, then you can add it. You need to traverse the whole array first to check all the elements.

var obj = {"id":3, "fname":"john", "lname":"doe"};
var userArray = [{
   "id": 1,
   "fname": "john",
   "lname": "doe"
}, {
   "id": 2,
   "fname": "john",
   "lname": "doe"
}];

/*Search for an user with the same id*/
var found = userArray.find(function(user) {
  return user.id == obj.id;
});

/*Add the user if not found*/
if(!found){
   userArray.push(obj); 
}

answered Jan 16, 2018 at 17:33

Javier Gonzalez

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Comments

jotaelesalinas · Accepted Answer · 2018-01-16 17:54:35Z

I see two possible solutions:

1) Checking that the id does not exist.

var exists = false;
userArray.forEach(function (element) { // n/2 checks on average
  if(element.id == obj.id) {           // (this specific awful code, always n checks)
    exists = true;
  }
});
if (!exists) {
  userArray.push(obj);
}

This code (or any improved loop-based version) iterates the array each time, that is why I prefer the second option.

2) Making userArray an object with the id as index.

var obj = {"id":1, "fname":"john", "lname":"doe"};
var userArray = {
  1: {
    "id": 1,
    "fname": "john",
    "lname": "doe"
  },
  2: {
    "id": 2,
    "fname": "john",
    "lname": "doe"
  }
};

if (typeof userArray[obj.id] === 'undefined') { // always 1 check
  userArray[obj.id] = obj;
}

console.log(userArray);

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