1const arrSum = arr => arr.reduce((a,b) => a + b, 0)

1console.log(
2  [1, 2, 3, 4].reduce((a, b) => a + b, 0)
3)
4console.log(
5  [].reduce((a, b) => a + b, 0)
6)

1const sum = arr => arr.reduce((a, b) => a + b, 0);

1arr.reduce((a, b) => a + b)

1function getArraySum(a){
2    var total=0;
3    for(var i in a) { 
4        total += a[i];
5    }
6    return total;
7}
8
9var payChecks = [123,155,134, 205, 105]; 
10var weeklyPay= getArraySum(payChecks); //sums up to 722

1arrSum = function(arr){  return arr.reduce(function(a,b){    return a + b  }, 0);}