How to add an input text field into a select element - select

Question

I try to develop a custom selectbox with „chosen“ (https://harvesthq.github.io/chosen/).
How can I achieve to add a single input text field ("Eigene Auflage") at the bottom of the opened select box which adds his value to the top, if someone clicks at it types something in. See image: )
Do I have to change the select/option into a ul/li ?
Here is my markup:
<select class="replace-select">
<option value="select-filled-1">Select Filled 1</option>
<option value="select-filled-2">Select Filled 2</option>
<option value="select-filled-3">Select Filled 3</option>
<option value="select-filled-4">Select Filled 4</option>
<option value="select-filled-5">Select Filled 5</option>
<option value="select-filled-6">Select Filled 6</option>
<option value="select-filled-7">Select Filled 7</option>
<option value="select-filled-8">Select Filled 8</option>
</select>

Answer 1

You can do this just by appending a text box to the chosen's created dropdown div, with events to add the contents of the text box to the original select. It's pretty much just a matter of using jQuery to append the box to the right element.
How it works is when you initialize chosen, it hides the select and creates a custom set of nested li's within a few divs. The dropdown div has class .chosen-drop, so you just need to use jQuery to select that element with $(".chosen-drop"), then append the text box to that using $.append(...). Your event handlers then just need to take the contents of that text box and add it to the original select.
$(document).ready(function() {
//initialize the chosen.
$("#chosenSelect").chosen({
width: "100px"
});
//append text box
$("#selectContainer .chosen-drop").append('<input class = "chosen-input"/>');
//click event for enter key
$('.chosen-input').bind("enterKey", function(e) {
//get value of text box, and add it to the select.
var newValue = $(".chosen-input").val();
//insert newValue into an option HTML with template literals
var optionHTML =`<option value="${newValue}">${newValue}</option>`;
$("#chosenSelect").prepend(optionHTML).trigger("chosen:updated");
//clear the textbox after adding to the select
$(".chosen-input").val("");
});
//watch for enter key
$('.chosen-input').keyup(function(e) {
if (e.keyCode == 13) {
$(this).trigger("enterKey");
}
});
});
.chosen-input {
width: 100%
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://harvesthq.github.io/chosen/chosen.jquery.js"></script>
<link href="https://harvesthq.github.io/chosen/chosen.css" rel="stylesheet" />
<div id="selectContainer">
<label>Press enter to add new item to select</label>
<br>
<select id="chosenSelect">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
</select>
</div>
Let me know if you need an explanation of any elements in my example.