binarySearch.js

function binarySearch(arr, x, index = 0) {
    if (arr.length == 0) {
        return -1;
    }

    let halfN = half(arr.length);
    
    if (arr[halfN] == x) {
        return index + halfN;
    }
    
    if (arr[halfN] < x) {
        return binarySearch(arr.slice(halfN), x, index + halfN);
    }
    
    return binarySearch(arr.slice(0, halfN), x, index);
}