Implement a function iSum that behaves just like rSum but instead of using recursion to implement the solution it uses iteration.

isum.js

//iSum(1) = 1                  => 1
// iSum(2) = 1 + 2              => 3
// iSum(3) = 1 + 2 + 3          => 6
// iSum(4) = 1 + 2 + 3 + 4      => 10
// iSum(5) = 1 + 2 + 3 + 4 + 5  => 15

var iSum = function(num){
 		var sum = 0;
	if(num > 0 ){
  		for(var i=1; i<=num; i++){
    	sum += i;
  		}
  }
  return sum; 
};

iSum(4);