My sollution with select dropdown and local storage

document.addEventListener('DOMContentLoaded', () => {
  const form = document.getElementById('registrar');
  const input = form.querySelector('input');
  const mainDiv = document.querySelector('.main');
  const ul = document.getElementById('invitedList');
  const div = document.createElement('div');
  const filterLabel = document.createElement('label');
  const filterCheckbox = document.createElement('input');
  const options = ["no response", "confirmed", "declined"]
  const setLiClassName = (li, select) => {
    if (select.value === "no response") { 
      li.className = '';
    } else {
      li.className = 'responded';
    }
  }
  const createLI = (text, response) => { //added response argument for management of the dropdown selection
    const li = document.createElement('li');
    const createElement = (elementName, property, value) => {
      const element = document.createElement(elementName);
      element[property] = value;
      return element;
    }
    const appendToLI = (elementName, property, value) => {
      const element = createElement(elementName, property, value);
      li.appendChild(element);
      return element;
    }
    const appendOptions = (select) => {
      for (let i = 0; i < options.length; i++) {
        let option = document.createElement('option');
        option.value = options[i];
        option.text = options[i];
        select.appendChild(option);
      }
      select.value = response; //sets response
      setLiClassName(li, select);
    }
    appendToLI('span', 'textContent', text);
    const select = appendToLI('select', 'id', 'select'); //added dropdown selection
    appendOptions(select);
    appendToLI('textarea', 'placeholder', 'enter your notes here');
    appendToLI('button', 'textContent', 'edit');
    appendToLI('button', 'textContent', 'remove');
    if (supportsLocalStorage()) {
      localStorage.setItem(text, response);     //saves text (name) and response to localStorage 
    }
    return li;
  }

  filterLabel.textContent = "Hide those who haven't responded";
  filterCheckbox.type = 'checkbox';
  div.appendChild(filterLabel);
  div.appendChild(filterCheckbox);
  mainDiv.insertBefore(div, ul);
  filterCheckbox.addEventListener('change', (e) => { 
    const isChecked = e.target.checked; 
    const lis = ul.children;
    if (isChecked) {
      for (let i = 0; i < lis.length; i++) {
        let li = lis[i];
        if (li.className === 'responded') {
          li.style.display = '';
        } else {
          li.style.display = 'none'; //hides lis if not answered
        }
      }
    } else { 
      for (let i = 0; i < lis.length; i++) {
        let li = lis[i];
        li.style.display = '';
      }
    }
  });

  form.addEventListener('submit', (e) => {
    e.preventDefault();
    const text = input.value;
    const checkForDuplicates = (text) => { //Checks for duplicates
      const names = Array.from(ul.querySelectorAll('span'));
        if (names.find(name => name.textContent == text)) { 
          return true;
        } else { 
          return false;
        }
      }
    if (!text) {
      input.placeholder = "Enter invitees' name here"; //checks if the string is empty
    } else if (checkForDuplicates(text)) {
      input.value = '';
      alert(`You've already invited ${text}!`);
    } else {
      input.value = ''
      const li = createLI(text, 'no response'); // sets select.value to "no response" for new invitees
      ul.appendChild(li);
      if (filterCheckbox.checked) {
        li.style.display = 'none'; //hides new lis if 'hide those who haven't responded' is checked
      }
    } 
  });

  ul.addEventListener('change', (e) => {
    let select = event.target;
    let li  = select.parentNode;
    setLiClassName(li, select);
    if (supportsLocalStorage()) {
      localStorage.setItem(li.firstElementChild.textContent, select.value); //updates select.value to localStorage 
    }
  });

  ul.addEventListener('click', (e) => {
    if (e.target.tagName === 'BUTTON') {
      const button = e.target;
      const li = button.parentNode;
      const ul = li.parentNode;
      const action = button.textContent;
      const select = li.querySelector('select');
      const nameActions = {
        remove: () => {
          ul.removeChild(li);
          if (supportsLocalStorage()) {
            localStorage.removeItem(li.firstElementChild.textContent); //removes from localStorage - make DRY? 
          }        
        },
        edit: () => {
          if (supportsLocalStorage()) {
            localStorage.removeItem(li.firstElementChild.textContent); //removes from localStorage - make DRY?
          }  
          const text = document.createElement('input')
          const span = li.firstElementChild;
          text.type = 'text';
          text.value = span.textContent;
          li.insertBefore(text, span);
          li.removeChild(span);
          button.textContent = 'save'
        },
        save: () => {
          const input = li.firstElementChild;
          const span = document.createElement('span');
          span.textContent = input.value;
          li.insertBefore(span, input);
          li.removeChild(input);
          button.textContent = 'edit';
          if (supportsLocalStorage()) {
            localStorage.setItem(span.textContent, select.value); //saves text (name) to localStorage with previous select.value
          } 
        }
      }
      // select & run action in button's name
      nameActions[action]();
    }
  });

  const supportsLocalStorage = () => {
    try {
    return 'localStorage' in window && window['localStorage'] !== null;
    } catch(e) {
      return false;
    }
  }


  window.onload = () => { //onload check supportsLocalStorage, load names and responses pairs, build lis with createLi() and ul.appendChild
    if (supportsLocalStorage()) { 
      const keys = Object.keys(localStorage);
      if (keys.length > -1) {
        for (let i = 0; i < keys.length; i++) {
          const li = createLI(keys[i], localStorage.getItem(keys[i])); 
          ul.appendChild(li);
        }
      }
    }  
  }

});