JavaScript Interview Prep: Find the unique element in an array where all elements but one occur twice

Prompt

Given an array of integers, where all elements but one occur twice, find the unique element

Solution

function lonelyinteger(a) {
    const aSort = a.sort();
    
    let unique = 0;
   for (let i=0; i < aSort.length; i=i+2){
       if (i+1<aSort.length && aSort[i] == aSort[i+1]){
           console.log("not unique", aSort[i]);
       } else {
           unique = aSort[i];
           break;
       }
   }
    console.log(unique);
    return unique;
}

console.log("1: ", lonelyinteger([1,2,3,4,3,2,1]));