如何下载用户创建的元素并给它一个事件？

Question

how to download an element created by the user and give it an event?

function tasks(e) {
    inputV = input.value;
    e.preventDefault();
    if (inputV !== "") {
        const ul = document.querySelector('.tasks-list');
        let li = document.createElement('li');
        li.innerHTML += inputV /*`<button class="deleteTasks">Usuń</button>`*/;
        ul.appendChild(li);
        let btnDell = document.createElement('button');
        btnDell.setAttribute("id", "deleteTasks");
        btnDell.innerHTML += 'usuń';
        li.appendChild(btnDell);
        input.value = "";
    }
};
add.addEventListener('click', tasks);

Answer 1

If I get it well you want your btnDell to delete the li element. You should use something like on the button click

function removeParent(e){
   e.parentNode.remove();
}

Answer 2

After creation of new list Element, you can attach your custom event handler.

function tasks(e) {
    inputV = input.value;
    e.preventDefault();
    if (inputV !== "") {
        const ul = document.querySelector('.tasks-list');
        let li = document.createElement('li');
        li.innerHTML += inputV /*`<button class="deleteTasks">Usuń</button>`*/;
        let node = ul.appendChild(li).cloneNode(true);
        node.addEventListener('click',(e)=>{
            e.preventDefault();
            let target = e.target;
            // put your logic here to execut on target after it being clicked
        },false); 
        let btnDell = document.createElement('button');
        btnDell.setAttribute("id", "deleteTasks");
        btnDell.innerHTML += 'usuń';
        li.appendChild(btnDell);
        input.value = "";
    }
};
add.addEventListener('click', tasks);

Edit I am editing this after reading your comment, please edit your question instead of put a comment to clarify your question. My assumption was that you want this functionality.

But it seems you'r logic on delete don't get execute on newly created items, if that's the case try to set a class property on each deletable li and write btnDell base on querySelectorAll that get all the elements at the time it's getting execute.