arrSum = function(arr){ return arr.reduce(function(a,b){ return a + b }, 0);}
const arrSum = arr => arr.reduce((a,b) => a + b, 0)
let nums = [1, 2, 3]; nums.reduce((curr, next) => curr + next);
[1,2,3,4,5].reduce((acc, current)=>acc+current, 0)