JavaScript - Copy Text Fields on Mouseup

First, to say that I am a novice in the use of JavaScript would be an understatement of the most egregious magnitude. I have PDF form where I'm attempting to allow the user to copy numerous fields into similar fields when a Checkbox is invoked (Mouseup). This is for use in a situation similar to the Order Name/Address - Ship To Name/Address information fields may (or may not) be identical. This is the code that I've embedded in the Javascript Editor box.



While these are clearly the efforts of an inspired amateur, from the research I was able to do myself - it seemed like the right code. On testing this (checking the Checkbox) though, nothing happens. Where did I step off the correct trail? Thanks!