Краен код на JavaScript

Ето крайният вариант на това, което трябва да получим:

cssbody {
  text-align: center;
}

#input, #list {
  display: inline-block;
}

#list {
  padding: 0;
  list-style-type: none;
}
#list span {
  margin-right: 5px;
}
#list .remove, #list .mark {
  color: blue;
  cursor: pointer;
}
#list .remove:hover, #list .mark:hover {
  text-decoration: underline;
}

#list .done .task {
  text-decoration: line-through;
}

html<div id="wrapper">
  <input id="input"><br>
  <ul id="list"></ul>
</div>

javascriptlet input = document.querySelector('#input');
let list = document.querySelector('#list');

input.addEventListener('keypress', function(event) {
  if (event.key == 'Enter') {
    let li = document.createElement('li');
    
    let task = document.createElement('span');
    task.classList.add('task');
    task.textContent = this.value;
    task.addEventListener('dblclick', function() {
      let text = this.textContent;
      this.textContent = '';
      
      let edit = document.createElement('input');
      edit.value = text;
      this.appendChild(edit);
      
      let self = this;
      edit.addEventListener('keypress', function(event) {
        if (event.key == 'Enter') {
          self.textContent = this.value;
        }
      });
    });
    li.appendChild(task);
    
    let remove = document.createElement('span');
    remove.textContent = 'изтрий';
    remove.classList.add('remove');
    remove.addEventListener('click', function() {
      this.parentElement.remove();
    });
    li.appendChild(remove);
    
    let mark = document.createElement('span');
    mark.textContent = 'изпълнено';
    mark.classList.add('mark');
    mark.addEventListener('click', function() {
      this.parentElement.classList.add('done');
    });
    li.appendChild(mark);
    
    list.appendChild(li);
    
    this.value = '';
  }
});

Результат: