Javascript Array findSortedFirst(sort_function)

Array.prototype.findSortedFirst = function(sort_function) {
    if (this.length == 0) {
     return null;
    }//from  www.jav  a  2s .com
    let smallest = this[0];
    for (let element of this) {
     if (sort_function(element, smallest) < 0) {
      smallest = element;
     }
    }
    return smallest;
};