duplicates-1.js

const nums = [2, 6, 3, 10]
const nums2 = [2, 4, 1, 2]

const duplicates = arr => {
  
  for (let i = 0; i < arr.length; i++) {
    for (let j = 0; j < arr.length; j++) {
      
      // If the indexes do not match but the 
      // values do, we have a duplicate!
      if (j !== i && arr[i] === arr[j]) {
        return true
      }
    }
  }
  
  // We looked at everything and no matches! 
  // There are no duplicates
  return false
}

console.log(duplicates3(nums))  // false
console.log(duplicates3(nums2)) // true