In what file I should include my code if I want content to come up on top of everything?

Question

I added a button and when you press on it new content should come up on top of everything, but if I icnlude my code into header.php it will cover only header, if I include in index.php it will cover only index, so my question is where I should include my code?

Answer 1

If you want to echo something extremely early, you can do that at template_redirect hook that runs before any template is processed. However that will effectively put output outside of proper markup and so markup produced will be invalid.

I do not quite understand why you need to actualyl output it early, if presentation is controlled with JavaScript (I assume?). You could as well echo it at end of page hidden and position/show when and how is needed on button pressed.

Answer 2

I guess what you need is wp_register_script() + wp_enqueue_script()

Are you talking about PHP or JavaScript??? Your description is simply not sufficient.