How do you convert jquery function to vanilla Javascript? [closed]

I am new to javascript and have a small snippet of code that I want to convert from jQuery to Javascript. Any pointers or can someone help?

A little background on the code – this is a function to toggle between tabs that populates different content when toggled. Here is the code:

  $("document").ready(function () {
    $(".tab-slider--body").hide();
    $(".tab-slider--body:first").show();
  });
  var tabSlider = document.querySelectorAll(".tab-slider--nav li");

  $(".tab-slider--nav li").click(function () {
    $(".tab-slider--body").hide();
    var activeTab = $(this).attr("rel");
    $("#" + activeTab).fadeIn();
    if ($(this).attr("rel") == "tab2") {
      $(".tab-slider--tabs").addClass("slide");
    } else {
      $(".tab-slider--tabs").removeClass("slide");
    }
    $(".tab-slider--nav li").removeClass("active");
    $(this).addClass("active");
  });