Currently working on a form which has two parts, outward and return (for journeys). You can choose to have either or both. When you first go to the page it simply says 'do you require an outward journey', and 'do you require a return journey', with a checkbox for each. So checking the outward one then displays the form for the outward journey details.
With me so far...?

So, if someone wants both an outward and return, most of the time their return journey details are going to be the same, but in reverse of the outward one. ie. the outward's destination will be the return's pickup, the outward's pickup will be the return's destination. Think of going to a pub in a taxi and then getting picked up and going back to where you started.
Therefore my assumption is, people are not going to want to have to fill out the same details twice. They complete the outward journey section, and then tick to say yes they want a return journey, and ideally when the return journey form displays it has the pickup point, destination a couple of other fields copied over from the outward one. This I can do.
However... how can I ensure that it only happens once? eg. if the visitor clicks to say yes they want a return journey, but actually they want to go elsewhere so they change the destination. Then cleverly they untick the 'I want a return journey' box. Realise what they've done and tick it again. I know I wouldn't be happy if my change had been lost and I had to do it again!
So, basically how can I ensure I only copy the form data over once, on the first time they say they want a return journey?
Sorry for waffling... I do that a lot

tia.