How to check if object value exists within a JavaScript array of objects and if not add a new object to array?

To check if object value exists within a JavaScript array of objects and if not add a new object to array, we use the some method.

For instance, we write

const arr = [
  { id: 1, username: "fred" },
  { id: 2, username: "bill" },
  { 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;
};

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

to define the add function.

Then we check if the entry with username equal to name exists with some.

If it returns false, then we call arr.push to append the object into the arr array.