Javascript autofill form field from another page

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Sorry but I know this isn't exactly a C5 issue.
I need to find a way of populating a single contact form field from a button click off another page. I have a site where people can book accommodation which goes to a standard form but the name of the accommodation needs to be filled out so the viewer doesn't have to choose again.
I found this:
http://jsfiddle.net/guyzyl/9stgu/...
which is what I am after but it needs to trigger from another page so viewers click a book button and it takes them to the booking form with accommodation already entered in a field.
My knowledge of javascript is pretty basic so any help appreciated.

trixiemay