const sum = arr => arr.reduce((a, b) => a + b, 0);
arrSum = function(arr){ return arr.reduce(function(a,b){ return a + b }, 0);}
[1, 2, 3, 4].reduce((a, b) => a + b, 0) // Output: 10
const arrSum = arr => arr.reduce((a,b) => a + b, 0)
function getArraySum(a){ var total=0; for(var i in a) { total += a[i]; } return total; } var payChecks = [123,155,134, 205, 105]; var weeklyPay= getArraySum(payChecks); //sums up to 722
const summation = (n) => (n * (n + 1)) / 2;
console.log( [1, 2, 3, 4].reduce((a, b) => a + b, 0) ) console.log( [].reduce((a, b) => a + b, 0) )