bootstrap4-dropdown-ml-hack-hover.js

$.fn.dropdown = (function() {
    var $bsDropdown = $.fn.dropdown;
    return function(config) {
        if (typeof config === 'string' && config === 'toggle') { // dropdown toggle trigged
            $('.has-child-dropdown-show').removeClass('has-child-dropdown-show');
            $(this).closest('.dropdown').parents('.dropdown').addClass('has-child-dropdown-show');
        }
        var ret = $bsDropdown.call($(this), config);
        $(this).off('click.bs.dropdown'); // Turn off dropdown.js click event, it will call 'this.toggle()' internal
        return ret;
    }
})();

$(function() {
    $('.dropdown [data-toggle="dropdown"]').on('click', function(e) {
        $(this).dropdown('toggle');
        e.stopPropagation(); // do not fire dropdown.js click event, it will call 'this.toggle()' internal
    });
    $('.dropdown').on('hide.bs.dropdown', function(e) {
        if ($(this).is('.has-child-dropdown-show')) {
        	$(this).removeClass('has-child-dropdown-show');
            e.preventDefault();
        }
        e.stopPropagation();    // do not need pop in multi level mode
    });
});

// for hover
$('.dropdown-hover').on('mouseenter',function() {
  if(!$(this).hasClass('show')){
    $('>[data-toggle="dropdown"]', this).dropdown('toggle');
  }
});
$('.dropdown-hover').on('mouseleave',function() {
  if($(this).hasClass('show')){
    $('>[data-toggle="dropdown"]', this).dropdown('toggle');
  }
});
$('.dropdown-hover-all').on('mouseenter', '.dropdown', function() {
  if(!$(this).hasClass('show')){
    $('>[data-toggle="dropdown"]', this).dropdown('toggle');
  }
});
$('.dropdown-hover-all').on('mouseleave', '.dropdown', function() {
  if($(this).hasClass('show')){
    $('>[data-toggle="dropdown"]', this).dropdown('toggle');
  }
});