smooth scrolling for all links and buttons on a pa

The first 26 lines give me smooth scrolling for all links in my navbar and my logo, but I don't know how to combine it with the scroll up button that I've got from another tutorial. Is there a way to make all links scroll in the first piece of code and not only elements in the navbar?

$(document).ready(function(){
  // Add scrollspy to <body>
  $('body').scrollspy({target: ".navbar", offset: 50});   

  // Add smooth scrolling on all links inside the navbar
  $("a").on('click', function(event) {
    // Make sure this.hash has a value before overriding default behavior
    if (this.hash !== "") {
      // Prevent default anchor click behavior
      event.preventDefault();

      // Store hash
      var hash = this.hash;

      // Using jQuery's animate() method to add smooth page scroll
      // The optional number (800) specifies the number of milliseconds it takes to scroll to the specified area
      $('html, body').animate({
        scrollTop: $(hash).offset().top
      }, 800, function(){

        // Add hash (#) to URL when done scrolling (default click behavior)
        window.location.hash = hash;
      });
    }  // End if
  });
});

jQuery(window).scroll(function(){
  if (jQuery(this).scrollTop() > 300) {
    jQuery('.scrollToTop').fadeIn();
  } else {
    jQuery('.scrollToTop').fadeOut();
  }
});

//Click event to scroll to top

jQuery('.scrollToTop').click(function(){
  jQuery('html, body').animate({scrollTop : 0},800);
  return false;
});

You need to separate click event for navigation bar link and your scrollToTop link, and register scrollToTop link to a click event as well. So your code will look like this (assuming you add a class 'nav-link' to links at the navbar):

$(document).ready(function(){
  // Add scrollspy to <body>
  $('body').scrollspy({target: ".navbar", offset: 50});   

  $('.scrollToTop').on('click',function(event){
      event.preventDefault();
    $('html, body').animate({scrollTop : 0}, 800);

  });

  // Add smooth scrolling on all links inside the navbar
  $(".nav-link").on('click', function(event) {
    // Make sure this.hash has a value before overriding default behavior
    if (this.hash !== "") {
      // Prevent default anchor click behavior
      event.preventDefault();

      // Store hash
      var hash = this.hash;

      // Using jQuery's animate() method to add smooth page scroll
      // The optional number (800) specifies the number of milliseconds it takes to scroll to the specified area
      $('html, body').animate({
        scrollTop: $(hash).offset().top
      }, 800, function(){

        // Add hash (#) to URL when done scrolling (default click behavior)
        window.location.hash = hash;
      });
    }  // End if
  });
});

jQuery(window).scroll(function(){
      if (jQuery(this).scrollTop() > 300) {
        jQuery('.scrollToTop').fadeIn();
      } else {
        jQuery('.scrollToTop').fadeOut();
      }
});