On it's face, this is a very odd request. I feel like, in trying to simplify the question, you've left out a lot of pertinent details.
My suspicion is that you have a specific problem you're trying to solve, and, due to lack of experience with web development, you've settled on this solution of using JS to copy an html snippet from one document to another, when a proper solution to the actual problem is probably nothing like that. Without knowing what the original problem is and what environment the code would be running in, I'm afraid it's going to be nearly impossible to offer any suggestions.