reduce sum

array_reduce_sum.js

let arr = [1,2,3,4,5,6,7,8,9,10];

// Array.prototype.reduce takes a function (reducer) and an initial value of type B
// and returns an value of type B
let num = arr.reduce(function (accum, value) {
  // The reducer function takes a value of 
  // type B and another value of the same type as the array (A)
  // returns a value of type B;
  
    return accum + value;
}, 0);
// the last argument is an initial value passed to the function;
console.log(num);
// 55