JSFiddle - React, Tailwind, and code Playground

JavaScript

foldl = function(xs, fn, init) {
    var result = init;
    if (xs === null) {return result;}
    for (var i=0; i<xs.length; i++) {
      result = fn(result, xs[i]);
    };
    return result;
  };    



sum = function(xs) {
    return foldl(xs, 
                 function(a,b) {
                     return a+b;
                 },
                 0);
};
  
prod = function(xs) {
    return foldl(xs, 
                 function(a,b) {
                     return a*b;
                 },
                 1);
};

var a = [1, 2, 3, 4, 5, 6];

y1 = sum(a);
y2 = prod(a);
alert(y1+", "+y2);