I have created a website with postgis, mapserver & openlayers. On the website you can enter a postal code and then a drivetime isochroon is created.
The problem now is that you can enter anything in the input box. If you enter a postal code that does not exist (or maybe some letters) nothing happens. No isochron is created, which is correct because it is not a valid code.
What I want is that if you enter a not existing postal code I would like to have a pop-up (or something like that) which says: 'this is not an existing postal code, please enter another postal code'
Someone any idea how I can create this?
The website is: maps.geodan.nl/reistijden.htm