Binary Search

let iterativeFunction = function (arr, x) {

    let start=0, end=arr.length-1;

    // Iterate while start not meets end
    while (start<=end){

        // Find the mid index
        let mid=Math.floor((start + end)/2);

        // If element is present at mid, return True
        if (arr[mid]===x) return true;

        // Else look in left or right half accordingly
        else if (arr[mid] < x)
             start = mid + 1;
        else
             end = mid - 1;
    }