Javascript null or empty control does not work

Javascript null or empty control does not work

I open this subject for second time.
However there is no solution.
Below code does not work. I can enter empty(Space) value.
var veri = {
YeniMusteriEkleTextBox: $('#YeniMusteriAdiTextbox_I').val(),
};
if (!veri.YeniMusteriEkleTextBox) {
alert("Customer name can not be empty!");
}