This recipe puts a trivial speed bump in the way of form spammers. By forcing them to actually evaluate the page with a Javascript engine (or do extra processing to figure out what is needed), you raise the amount of effort required above that which most form spammers are likely to spend.
Pick a nice random number. The SHA1 of some Git commit would be a good one. I picked this one:
5187b6aec9b0607858a7c032d2c9ded04b050f31
Step 2