gist-cv.js

function indexEqualsValue(a) {
    let left = 0;
    let right = a.length - 1;
    let mid;
    while (left != right) {
        mid = Math.floor(((right - left) / 2) + left);

    if (mid <= a[mid]) {
        right = mid;
    } else {
        left = mid + 1;
    }
      }
    return left == a[left] ? left : -1
}