How to refresh a div with PJAX?

Sorry by advance if i didn’t post the message in the good topic.
I need to refresh a div with PJAX. I don’t know PJAX at all (i know how to do it with AJAX).
I searched how to do, i found a script but it doesn’t work, I am totally lost.

function pjaxReload(here_the_div_to_refresh) {
  var defaults = {
    url: here_the_url_to_the_file_where_is_the_div_to_refresh,
    push: false,
    replace: true,
    scrollTo: false
  return pjax($.extend(defaults, optionsFor(here_the_div_to_refresh)))

If someone can help me it would be nice