We should be ashamed of ourselves. All the web resources for reverse complementing a piece of DNA are straight from the 90s, requiring a round trip to the server and opening a new window. We can do better. (I'm not linking to any examples on purpose).
Personally, I think we should be ashamed with ourselves if we have to use a web-browser to reverse complement a sequence.
OK, so its client side but its not dynamic, right?
You mean copy and paste of sequence in the Textarea form should automatically generate reserve complement? Or if I keep on typing sequences in the Textarea should keep on generating reserve strand?
Personally I do not like another window with results popping out at the other corner of the screen but this is probably a matter of taste.
If you need to reverse complement a sequence as part of an application/pipeline, or if the sequence is large, I agree with GWW - you shouldn't consider a web solution (too slow, consumes network bandwidth). For once-off small tasks, I see nothing wrong with a web tool for convenience. @Casbon, if people are going to use the tool for small sequences, I don't think there is an urgent need for a completely client-side solution - savings are minimal. Out of interest, why are you asking the community to write this? Do you intend to make it available on a server?
When we look for troubles in alignments etc., having a web page like this would be convenient.
Writing a code reverse complement may look trivial, but if you do not want your tool to be substandard, please consider the features that a current user normally expacts: the correct handling of nucleotide ambiquity codes, preserving upper/lowercase, handling spaces/numbers/newlines/FASTA header as expected and the like.