Check if object value exists within a Javascript array of objects and if not add a new object to array

Question

I've assumed that ids are meant to be unique here. some is a great function for checking the existence of things in arrays:

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

function 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;
}

console.log(add(arr, 'ted'));

It's rather trivial to check for existing username:

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

function userExists(username) {
  return arr.some(function(el) {
    return el.username === username;
  }); 
}

console.log(userExists('fred')); // true
console.log(userExists('bred')); // false

But it's not so obvious what to do when you have to add a new user to this array. The easiest way out - just pushing a new element with id equal to array.length + 1:

function addUser(username) {
  if (userExists(username)) {
    return false; 
  }
  arr.push({ id: arr.length + 1, username: username });
  return true;
}

addUser('fred'); // false
addUser('bred'); // true, user `bred` added

It will guarantee the IDs uniqueness, but will make this array look a bit strange if some elements will be taken off its end.

This small snippets works for me..

const arrayOfObject = [{ id: 1, name: 'john' }, {id: 2, name: 'max'}];

const checkUsername = obj => obj.name === 'max';

console.log(arrayOfObject.some(checkUsername))

if you have array of elements like ['john','marsh'] then we can do some thing like this

const checkUsername = element => element == 'john';
    
console.log(arrayOfObject.some(checkUsername))

This is what I did in addition to @sagar-gavhane's answer

const newUser = {_id: 4, name: 'Adam'}
const users = [{_id: 1, name: 'Fred'}, {_id: 2, name: 'Ted'}, {_id: 3, name:'Bill'}]

const userExists = users.some(user => user.name === newUser.name);
if(userExists) {
    return new Error({error:'User exists'})
}
users.push(newUser)

I think that, this is the shortest way of addressing this problem. Here I have used ES6 arrow function with .filter to check the existence of newly adding username.

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

function add(name) {
    var id = arr.length + 1;        
            if (arr.filter(item=> item.username == name).length == 0){
            arr.push({ id: id, username: name });
        }
}

add('ted');
console.log(arr);

Link to Fiddle

There could be MULTIPLE POSSIBLE WAYS to check if an element(in your case its Object) is present in an array or not.

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

let say you want to find an object with id = 3.

1. find: It searches for an element in an array and if it finds out then it returns that element else return undefined. It returns the value of the first element in the provided array that satisfies the provided testing function. reference

const ObjIdToFind = 5;
const isObjectPresent = arr.find((o) => o.id === ObjIdToFind);
if (!isObjectPresent) {            // As find return object else undefined
  arr.push({ id: arr.length + 1, username: 'Lorem ipsum' });
}

2. filter: It searches for elements in an array and filters out all element that matches the condition. It returns a new array with all elements and if none matches the condition then an empty array. reference

const ObjIdToFind = 5;
const arrayWithFilterObjects= arr.filter((o) => o.id === ObjIdToFind);
if (!arrayWithFilterObjects.length) {       // As filter return new array
  arr.push({ id: arr.length + 1, username: 'Lorem ipsum' });
}

3. some: The some() method tests whether at least one element is present in an array that passes the test implemented by the provided function. It returns a Boolean value. reference

const ObjIdToFind = 5;
const isElementPresent = arr.some((o) => o.id === ObjIdToFind);
if (!isElementPresent) {                  // As some return Boolean value
  arr.push({ id: arr.length + 1, username: 'Lorem ipsum' });
}

Let's assume we have an array of objects and you want to check if value of name is defined like this,

let persons = [ {"name" : "test1"},{"name": "test2"}];

if(persons.some(person => person.name == 'test1')) {
    ... here your code in case person.name is defined and available
}