JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" type="text/css" media="screen" href="main.css" />
    <script src="https://code.jquery.com/jquery-1.10.2.js"></script>
    
</head>
<body>
    
        <input type="text" id="shelfname"/>
        <input type="button" id="btn_addShelf" value="Добавить полку">   
     <div id="bookshelf">
        <h1 class="bookshelf_name"></h1>
    </div>
    
</body>
<script src="script.js"></script>
</html>

JavaScript

var library = [];
var bookshelf = function(name,books) {
    this.name = name;
    this.books = books;
    
}

var bookshelf_div = document.getElementById('bookshelf');



window.onload = function(){



    $(document).on('click','#btn_addBook',function(e){
        e.preventDefault();
        var rel = this.rel;
         //or using attr()
        var rel=$(this).attr('rel'); 
        var book = document.getElementById('name').value
        console.log(this.tagName);
      });

    function searchShelfName(searchName){
        var objelem = document.getElementsByTagName('div');
        var elements = Object.values(objelem);
        var flag = false;
        for(var i = 0; i < elements.length; i++){
            var names = elements[i].getElementsByTagName('h1')[0].innerHTML;
            if (searchName == names) {
                flag = true;
            }
        }
        return flag;
    }

        

    function addBookshelf(){
        var shelfname = new bookshelf(document.getElementById('shelfname').value,[]);
        if (!searchShelfName(shelfname.name)){
            library.push(shelfname);
            var str = '<div id="bookshelf"><h1 class=bookshelf_name>' + shelfname.name + '</h1><input type="text" id="bookname"/><p id="btn_addBook">add</p></div>';
            document.getElementById('bookshelf').innerHTML += str;
        } else alert('Такая полка уже существует!');


    }

    document.getElementById('btn_addShelf').onclick = addBookshelf;


    //document.getElementById('btn_addBook').onclick = addBookName;

};