sum all elements in array javascript

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

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

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

array.reduce((a, b) => a + b, 0)