JSFiddle - React, Tailwind, and code Playground

JavaScript

Array.prototype.sum = function(predicate){
    predicate = predicate || function(match){
        if(typeof match =="string"){
             return match.length;
        }
        return match;
    };
    var result = 0;
    for (var i = 0; i < this.length; i++) {
       result += predicate(this[i]);
    }    
    return result;
};
var array1 = ["hello","world"];
console.log(array1.sum());
var array2 = [10,20,30];
console.log(array2.sum());