[JAVA] Implementation of category pull-down function

In the final assignment of a certain programming school, I implemented a category pull-down function (a function that displays the category by pulling down when you touch the word category in the header of the top page), so I explained it for my own output as well. I think

Immediately, the flow of pull-down function implementation is as follows.

① Touch the letters of the category

② An event occurs in jQuery and the link attached to the category is read.

③ Perform Ajax communication with that link, first get the parent category from the database and return the value in json format.

④ After that, just reassemble the acquired data into HTML form and add it under the characters of the category.

⑤ The child elements are displayed in the same flow as above, and are not displayed when the grandchild elements are reached.

The source code that realized this is as follows. (Only the relevant part is extracted)

   .contents__bottom
      .header-bottom-left
        .header-bottom-left-category
          = link_to "Category", api_category_path(0) ,class: "category_name", id: "catroy_top_title"
          .header-bottom-left-category-field    

$(function(){
  
  //Generate pull-down HTML
  function buildHTML(data){

    var html = $("<div>").addClass("header-bottom-left-category-field-nav")
    var link

    data.forEach(function(value){
      link = $("<a>", {
        href: "/api/categories/" + value.id ,
        "class":"category_name"
      }).text(value.name)
      link = $("<p>").append(link)

      html.append(link)
    })

    return html
  }

  //If you touch the title of the category, it will be displayed again from the beginning
  $("#catroy_top_title").mouseenter(function(){
    $(".header-bottom-left-category-field-nav").remove()
  })

   //Activated when the mouse is released
   $(".header-bottom-left-category").mouseleave(function(){
    $(".header-bottom-left-category-field-nav").remove()
  })

  $(document).on({

    //Starts when the cursor is over
    'mouseenter' : function() {

      //Get the category path
      var path = $(this).attr("href");

      //Get the child elements of the touched category
      $.ajax({
        url: path,
        type: "GET",
        dataType: "json",
        context:this,
        cache: false,
      })
      .done(function(result){
  
        //Do not show choices if there are no child elements
        if( result.length != 0 ){
  
          //Add a new form below the selected form
          var html = buildHTML(result)

          //Delete any list that was added earlier
          $(this).parent().parent().nextAll(".header-bottom-left-category-field-nav").remove()
          $(".header-bottom-left-category-field").append(html)

        } 

      })

      //Activated when the mouse is released
      $(".header-bottom-left-category-field-nav").mouseenter(function(eo){ 
        $(this).find("a").css("color","")
      })

    },'mouseleave' : function(){

       //Activated when the mouse is released
      $(".header-bottom-left-category-field-nav").mouseleave(function(eo){
        $(eo.fromElement).css("color","orange")
      })
     
    }
  }, ".category_name") 

})

namespace :api do
  resources :categories, only: [:show]
end

class Api::CategoriesController < ApplicationController
 
  def show

    if params[:id] == "0"
      @categories = Category.where(ancestry:nil)
    else
      @categories = Category.find(params[:id]).children
    end

    respond_to do |format|
      format.html{
        if params[:id] == "0"
          redirect_to category_all_items_path
        else
          redirect_to category_all_items_path(category_id: params[:id])
        end
      }
      format.json{
        render json: @categories
      }
    end 

  end

end

(*) Please use it after making it suitable for your environment.