How to create a dependent dropdown in Ruby on Rails

How to create a dependent dropdown in Ruby on Rails?

In the form as is

<%= f.select(:project_id, Project.all.collect {|p| [p.name, p.id]},  {prompt: "Select"}, {class: 'form-control'}) %>
<%= f.select(:task_id, Tasks.all.collect {|t| [t.name, t.id]}, {}, {class: 'form-control'}) %>

and those fields generated HTML is

<select class="form-control" name="hour[project_id]" id="hour_project_id">
    <option value="">Select</option>
    <option value="1">Real Estate</option>
    <option value="2">Time Sheet App</option>
</select>

<select class="form-control" name="hour[task_id]" id="hour_task_id" disabled="">
    <option value="3">Developer</option>
    <option value="4">Design</option>
    <option value="6">Backend</option>
</select>

that’s it in the form, now JS, Ajax & controller

The JS / Ajax is

$("#hour_task_id").prop("disabled", true); // second dropdown is disable while first dropdown is empty
$("#hour_project_id").change(function(){
  	var project = $(this).val();
  	if(project == ''){
  		$("#hour_task_id").prop("disabled", true);
  	}else{
  		$("#hour_task_id").prop("disabled", false);
  	}
  	$.ajax({
	    url: "/tasks",
	    method: "GET",  
	    dataType: "json",
	    data: {project: project},
	    error: function (xhr, status, error) {
	      	console.error('AJAX Error: ' + status + error);
	    },
	    success: function (response) {
	      	console.log(response);
	      	var tasks = response["tasks"];
	      	$("#hour_task_id").empty();

	      	$("#hour_task_id").append('<option>Select Task</option>');
	      	for(var i = 0; i < tasks.length; i++){
	      		$("#hour_task_id").append('<option value="' + tasks[i]["id"] + '">' +tasks[i]["name"] + '</option>');
	      	}
	    }
  	});
});

and in the controller into action

if params[:project].present?
    @tasks = Project.find(params[:project]).tasks
else
    @tasks = Task.all
end
if request.xhr?
    respond_to do |format|
        format.json {
            render json: {tasks: @tasks}
        }
    end
end

That’s it