How to count empty lines inside a string in javascript

I'm trying to count all the empty lines inside a string. My current function kind of works:

function count_empty(text) {
    var regex = /\r\n?|\n/g;
    var lines = text.split(regex);
    var sep = [];
    $.each(lines, function(k, val) {
        if(!val) {
            //sentence
            sep.push(val);
        }
    });
    return sep.length;
}

...but I really think it could be achieved with a far better approach with something like this:

function count_empty(text) {
    return (text.match(/\r\n?|\n/g) || []).length;
}

Of course, the regex in the 2nd alternative should be retouched to actually accomplish the requirements. So, the question is: What regex should I use in the second approach to retrieve the blank lines only?

One consideration: If a line contains whitespaces only, it will be treated as an empty line.

This textarea's string should return 3 with the function.

<textarea id="test">first line

third line


</textarea>

Thanks!