Given an array of size 3X+1, where every element occurs three times, except one element, which occurs only once. Find the element that occurs only once. code example

Example 1: Given an array of integers, every element appears thrice except for one which occurs once.

let contacts = new Map()
contacts.set('Jessie', {phone: "213-555-1234", address: "123 N 1st Ave"})
contacts.has('Jessie') // true
contacts.get('Hilary') // undefined
contacts.set('Hilary', {phone: "617-555-4321", address: "321 S 2nd St"})
contacts.get('Jessie') // {phone: "213-555-1234", address: "123 N 1st Ave"}
contacts.delete('Raymond') // false
contacts.delete('Jessie') // true
console.log(contacts.size) // 1

Example 2: create a function that takes in an array of numbers and returns only the number that are even after 1 is added to the value

const evenAfter = (arr) => {
    let i = 0
    let newArr = []
    while (i <= arr.length) {
        if ((arr[i] + 1) % 2 === 0){          
            newArr.push(arr[i])
        }  
        i++
    }
    return newArr
}

console.log(evenAfter([3,6,7,8,9,11]))