// method to extend String to call reduce the same way as an Array
String.prototype.reduce = function () { 
    return this.split().reduce(...arguments);
}

// sum of the ascii codes using the newly created String prototype method
str.reduce((a,b) => a + b.charCodeAt(0), 0);

let str = "hello";
// reduce string to the sum of the ascii codes of its characters
str.split().reduce((a,b) => a + b.charCodeAt(0), 0);