function binarySearch(arr, target) {
    let left = 0;
    let right = arr.length - 1;
    while (left < right) {
        let mid = left + Math.floor((right - left) / 2);
        if (arr[mid] === target) {
            return mid;
        }
        if (arr[mid] < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    return left;
}

console.log(binarySearch([1, 2, 3, 10], 1) === 0)
console.log(binarySearch([1, 2, 3, 10], 2) === 1)
console.log(binarySearch([1, 2, 3, 10], 3) === 2)
console.log(binarySearch([1, 2, 3, 10], 10) === 3)
console.log(binarySearch([1, 2, 3, 10], 9) === 3)
console.log(binarySearch([1, 2, 3, 10], 4) === 3)
console.log(binarySearch([1, 2, 3, 10], 0) === 0)
console.log(binarySearch([1, 2, 3, 10], 11) === 3)
console.log(binarySearch([5, 7, 8, 10], 3) === 0)