Print only negative numbers and its sum aplaying loops and arrays

I need help with a program, I have to use a loop to output all negative integers and their sum. I should use just basic method.

Negative integers: -2, -1, -7 <----//No comma at the end.

Sum negative nums: -10

When I run my program the last integers has an additional comma at the end, I can’t take it out with “if (i != array.length-1)” because the last element in my array is positive but the loop analyze that there is a empty element. How I can remove that comma in a logical way. The result have to be print inside a loop separate by comma space: (", ").

function negativeArray(array)
    {
        document.write("Negative integers: ")
        for (var i = 0, count = 0; i < array.length; i++) 
        {
            if (array[i] != undefined && array[i] < 0){
                    document.write(array[i]);
                    count += array[i];
                    if (i != array.length-1) document.write(", ")}
        }
            document.write( "<br>Sum negative nums: " + count)
    }
        var items = [1, -2, 3, 4 -5, 6, -7, 8];
        negativeArray(items);