Dominator

An array A consisting of N integers is given. The dominator of array A is the value that occurs in more than half of the elements of A.

For example, consider array A such that
A[0] = 3 A[1] = 4 A[2] = 3
A[3] = 2 A[4] = 3 A[5] = -1
A[6] = 3 A[7] = 3

The dominator of A is 3 because it occurs in 5 out of 8 elements of A (namely in those with indices 0, 2, 4, 6 and 7) and 5 is more than a half of 8.

Write a function
function solution(A);
that, given an array A consisting of N integers, returns index of any element of array A in which the dominator of A occurs. The function should return −1 if array A does not have a dominator.

For example, given array A such that
A[0] = 3 A[1] = 4 A[2] = 3 A[3] = 2 A[4] = 3 A[5] = -1 A[6] = 3 A[7] = 3 the function may return 0, 2, 4, 6 or 7, as explained above.

Write an efficient algorithm for the following assumptions:
• N is an integer within the range [0..100,000];
• each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].

function solution(A) {
    // write your code in JavaScript (Node.js 8.9.4)
    if(A.length<1) return -1
    
    A1 = A.slice()
    A1.sort((a,b)=>a-b)
    const h = Math.floor(A1.length/2) // middle index
    const d = A1[h]
    
    let res = [], count = 0
    for(let i=0; i<A.length; i++){
        if(A[i]==d){
            res.push(i)
            count ++
        }
    }
    //console.log(res)
    if( count > h ) return res[0]
    else return -1
}