End date should be always greater than start date

function onChange(control, oldValue, newValue, isLoading) {
if (isLoading || newValue == '') {
return;
}
 //Type appropriate comment here, and begin script below
var startDate = new Date(g_form.getValue('start_date')); //get the value of the start_date field using the g_form.getValue method
var checkEnd = new Date(newValue); // create a new JS date from the desired end_date field (using newValue parameter)
 if (checkEnd <= startDate){ //Again - a simple JS Date object comparison
alert('End date must be after start date');
g_form.setValue('end_date','');
}
}