Arrays

Add, subtract, multiply stuff.

https://www.w3schools.com/jsref/jsref_reduce.asp

array.reduce(function(total, currentValue, currentIndex, arr), initialValue)

Add up items

var stuff = [10,15,5,20]

var totalstuff = stuff.reduce(addup,0);

function addup(total, currentval) {
  return total + currentval;
}

Same thing

var stuff = [10,15,5,20]

var totalstuff = stuff.reduce(function(total, currentval) {
  return total + currentval;
},0);

Same thing

var stuff = [10,15,5,20]

var totalstuff = stuff.reduce((total, currentval)=> total + currentval , 0);