testIfExistsByBinarySearch.js

function testIfExistsByBinarySearch(a, x) {
    let il = 0;
    let ir = a.length;
    while (il < ir) {
        const midIndex = Math.floor((ir + il) / 2);
        const midValue = a[midIndex];
        if (midValue < x) {
            // search right half
            il = midIndex + 1
        } else if (midValue > x) {
            // search left half
            ir = midIndex;
        } else {
            return true;
        }
    }
    return false;
}