JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" class="out" id="typps" value=""placeholder="Click to open" readonly>
		<div id="select_type">
			<ul>
				<li><input type="checkbox" name="type[]" class="sel_types" id="hodnota1" value="hodnota1">hodnota1</li>
				<li><input type="checkbox" name="type[]" class="sel_types" id="hodnota2" value="hodnota2">hodnota2</li>
				<li><input type="checkbox" name="type[]" class="sel_types" id="hodnota3" value="hodnota3">hodnota3</li>
			</ul>
		</div>
                    
<br>     <br>               
 <select name="day" id="day" multiple="multiple" >
          <option>Day</option>
          <option value="mon">Monday</option>
          <option value="tue">Tuesday</option>
          <option value="wed">Wednesday</option>
          <option value="thu">Thursday</option>
          <option value="fri">Friday</option>
          <option value="sat">Saturday</option>
          <option value="sun">Sunday</option>
        </select>

CSS

#select_type{display:none;}
#select_type ul{padding:0}
#select_type li{list-style:none;}

JavaScript

$("#typps").click(function() {
		 $("#select_type").toggle();
		 
		});
		



$(':checkbox.sel_types').on('change', function() {
    var assignedTo = $(':checkbox.sel_types:checked').map(function() {
        return this.id;
    })
    .get();
	
	 var value = assignedTo;
     var input = $('.out');
     input.val(value);
    
    
});