SOURCE

/**
 * @param {number} x
 * @return {number}
 */
var mySqrt = function (x) {
    let start = 0;
    let end = x;
    let mid = Math.floor((start + end) / 2);
    if (x === 1) return 1;
    while (start < mid) {
        if (mid ** 2 === x) {
            break;
        }
        if (mid ** 2 > x) {
            end = mid;
            mid = Math.floor((start + end) / 2);
        }
        if (mid ** 2 < x) {
            start = mid;
            mid = Math.floor((start + end) / 2);
        }
    }
    return mid
};
console.log(mySqrt(8));