How to Check if an Object Value Exists within a JavaScript Object Array and if not, Add a New Object into the Array?

Sometimes, we want to check if an object value exists within a JavaScript object array and if not, add a new object into the array.

In this article, we’ll look at how to check if an object value exists in an array and insert a new entry if it doesn’t exist.

Using the Array.prototype.some Method

We can use the some JavaScript method to check if an entry with the given condition exists in a JavaScript array.

And we can use the push method to add a new entry into the array.

To use it to check if an entry with the given condition exists and add an entry if it doesn’t exist, we can write:

const arr = [{
  id: 1,
  username: 'fred'
}, {
  id: 2,
  username: 'bob'
}, {
  id: 3,
  username: 'ted'
}];

const add = (arr, name) => {
  const {
    length
  } = arr;
  const id = length + 1;
  const found = arr.some(el => el.username === name);
  if (!found) {
    arr.push({
      id,
      username: name
    });
  }
  return [...arr];
}

const newArr1 = add(arr, 'ted')
const newArr2 = add(arr, 'james')
console.log(newArr1);
console.log(newArr2);

We have the arr array which we want to check if an entry with the given username exists and add a new entry with the given username if it doesn’t.

To do this, we create the add function that takes the arr array to check and the name to look up.

In the function, we get the length of arr and set the id to length + 1 .

Then we call arr.some with a callback that returns whether the el array entry meets the condition el.username === name and assign the result to found

If found is false , that means an entry with username equal to the name doesn’t exist.

And so we call arr.push with a new entry with the given name as the username .

Then we return a copy of arr to make sure we don’t modify the original arr array.

Therefore, newArr1 is:

[
  {
    "id": 1,
    "username": "fred"
  },
  {
    "id": 2,
    "username": "bob"
  },
  {
    "id": 3,
    "username": "ted"
  }
]

And newArr2 is:

[
  {
    "id": 1,
    "username": "fred"
  },
  {
    "id": 2,
    "username": "bob"
  },
  {
    "id": 3,
    "username": "ted"
  },
  {
    "id": 4,
    "username": "james"
  }
]

Conclusion

We can use the some JavaScript method to check if an entry with the given condition exists in a JavaScript array.

And we can use the push method to add a new entry into the array.