var arr = [1,2,3,4,5,6,7,8,9,10]

function binarySearch(elem, arr) {
    //loop through array and partition
    var max = arr.length - 1,
        min = 0,
        mid = arr[Math.floor(len/2)];

    if (arr.length === 0){
        return "Key not found, array is empty";
    }
    else if (elem === arr[max]){
        return max;
    }
    else if (elem === arr[min]) {
        return 0;
    }
    //perform the binary search here
    else {
        while(min < max) {
            if(elem > arr[mid]) {
                //move your min up, niqqa
                min = mid + 1;
            }
            else {
                //partition up to mid
                max = mid;
            }

        }

        if((arr[min] === elem)&&(max === min)){
            return min;
        } else {
            return "Key not found in array, you're searching for shit";
        }
    }
}

binarySearch(4, arr);