I am trying to remove all the jQuery from my code and I cannot find the vanilla javascript equivalent of this:

post_template=document.getElementById('post_template')
$("#modal-body").html(post_template);

I've tried the following, but it does not work:

post_template=document.getElementById('post_template')
document.getElementById('modal-body').html=post_template

If someone has a website that can show me all the methods of the getElementById object that would be super useful...Surprisingly all the documentation I've found doesn't explain all the options I can put after getElementById.