Toggle from light to dark move using slider is not working

Please see my code below. I am trying just to get my existing slider to toggle between light and dark mode. I am using typescript, HTML, and CSS. I was easily able to get this to work with a button, but I am trying to do it with a slider.

I have tried to use the .checked attribute, just the eventlistener as well as a boolean to detect whether the page is currently dark or light. I have seemingly tried everything, in addition to talking to chatgpt. Nothing seemed to work. I would appreciate any help here.

Please see all code below.

const themeStyle = document.getElementById('theme-style');

// Detect if slider has been toggled on or off
const sliderToggle = document.getElementById('toggle-switch') //as HTMLInputElement;

// Show message when general button is interacted
function showMessage() {
  console.log("showMessage function called");
  const message = "Hello, TypeScript!";
  alert(message);
}

// Button interaction for general button
const button = document.getElementById("general-button");

function generalButtonSetUp() {
  if (button) {
    button.addEventListener("click", showMessage);
  }
}

// Switch for theme change
function themeSwitchSetUp() {
  let body = document.body;
  if (sliderToggle) {
    sliderToggle.addEventListener('change', () => {
      if (sliderToggle.checked) {
        body.classList.add('light-theme');
      } else {
        body.classList.remove('light-theme');
      }
    });
  }
}

// Check for element existence before attaching event listeners
document.addEventListener("DOMContentLoaded", () => {
  generalButtonSetUp();
  themeSwitchSetUp();
});

body {
  background-color: #333333;
  color: #ffffff;
}

.light-theme {
  background-color: #ffffff;
  color: #000000;
}

.switch {
  position: relative;
  display: inline-block;
  width: 60px;
  height: 34px;
}

.switch input {
  opacity: 0;
  width: 0;
  height: 0;
}

.slider {
  position: absolute;
  cursor: pointer;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: #ccc;
  -webkit-transition: .4s;
  transition: .4s;
}

.slider:before {
  position: absolute;
  content: "";
  height: 26px;
  width: 26px;
  left: 4px;
  bottom: 4px;
  background-color: white;
  -webkit-transition: .4s;
  transition: .4s;
}

input:checked + .slider {
  background-color: #2196F3;
}

input:focus + .slider {
  box-shadow: 0 0 1px #2196F3;
}

input:checked+.slider:before {
  -webkit-transform: translateX(26px);
  -ms-transform: translateX(26px);
  transform: translateX(26px);
}

.slider.round {
  border-radius: 34px;
}

.slider.round:before {
  border-radius: 50%;
}

<body>
  <h1>Welcome to My TypeScript Webpage</h1>
  <p>This is a basic webpage using TypeScript.</p>

  <label id="toggle-switch" class="switch">
            <input type="checkbox">
            <span class="slider round"></span>
        </label>

  <button id="general-button">General Button</button>

  <script src="dist/app.js"></script>
</body>

Solution

The issue is with your sliderToggle. To make your code work; you need addEventListener on input rather than toggle-switch label. Something like:

const themeStyle = document.getElementById('theme-style');

// Detect if slider has been toggled on or off
const sliderToggle = document.querySelector('#toggle-switch input')
// ^^^^^^^^^^Notice this

// Show message when general button is interacted
function showMessage() {
  console.log("showMessage function called");
  const message = "Hello, TypeScript!";
  alert(message);
}

// Button interaction for general button
const button = document.getElementById("general-button");

function generalButtonSetUp() {
  if (button) {
    button.addEventListener("click", showMessage);
  }
}

// Switch for theme change
function themeSwitchSetUp() {
  let body = document.body;
  if (sliderToggle) {
    sliderToggle.addEventListener('change', () => {
      if (sliderToggle.checked) {
        body.classList.add('light-theme');
      } else {
        body.classList.remove('light-theme');
      }
    });
  }
}

// Check for element existence before attaching event listeners
document.addEventListener("DOMContentLoaded", () => {
  generalButtonSetUp();
  themeSwitchSetUp();
});

body {
  background-color: #333333;
  color: #ffffff;
}

.light-theme {
  background-color: #ffffff;
  color: #000000;
}

.switch {
  position: relative;
  display: inline-block;
  width: 60px;
  height: 34px;
}

.switch input {
  opacity: 0;
  width: 0;
  height: 0;
}

.slider {
  position: absolute;
  cursor: pointer;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: #ccc;
  -webkit-transition: .4s;
  transition: .4s;
}

.slider:before {
  position: absolute;
  content: "";
  height: 26px;
  width: 26px;
  left: 4px;
  bottom: 4px;
  background-color: white;
  -webkit-transition: .4s;
  transition: .4s;
}

input:checked+.slider {
  background-color: #2196F3;
}

input:focus+.slider {
  box-shadow: 0 0 1px #2196F3;
}

input:checked+.slider:before {
  -webkit-transform: translateX(26px);
  -ms-transform: translateX(26px);
  transform: translateX(26px);
}

.slider.round {
  border-radius: 34px;
}

.slider.round:before {
  border-radius: 50%;
}

<body>
  <h1>Welcome to My TypeScript Webpage</h1>
  <p>This is a basic webpage using TypeScript.</p>

  <label id="toggle-switch" class="switch">
            <input type="checkbox">
            <span class="slider round"></span>
        </label>

  <button id="general-button">General Button</button>

  <script src="dist/app.js"></script>
</body>