javascript实现二分查找失败是为什么？

Question

实现代码:

Array.prototype.binary_search = function(low, high, key) {
    var mid = parseInt((high + low) / 2),
          low = low,
          high = high,
          key = key;
    if(low > high)
        return -1;
    else {
        if(key == this[mid])
            return mid;
        else if(key > this[mid])
            this.binary_search(mid+1, high, key);
        else
            this.binary_search(low, mid-1, key);
    }
}