How to check whether the items are unique in an array using JavaScript

Question

If you have an array with primitive values as per below;

const arr = [1, 2, 3, 4, 45, 4, 66, 3];

Is there a more efficient way to check whether all the items are unique rather than iterating all items as below?

let newArr = [];
let isUnique = true;
arr.forEach(item => 
{
   if(newArr.indexOf(item) != -1)
   {
       isUnique = false;
       break;
   }
   newArray.push(item);
});

Answer 1

An indexOf in a forEach is O(n ^ 2) . I'd use a Set instead - Set.has is O(1) (overall complexity of O(n) ):

const allAreUnique = (arr) => {
  const set = new Set();
  for (const item of arr) {
    if (set.has(item)) return false;
    set.add(item);
  }
  return true;
};

 const allAreUnique = (arr) => { const set = new Set(); for (const item of arr) { if (set.has(item)) return false; set.add(item); } return true; }; console.log(allAreUnique([1, 2, 3, 4, 45, 4, 66, 3])); console.log(allAreUnique([1, 2, 3, 4, 45, 66]));