// Function To get all formdata values including multioption values

function handleSubmit(event) {

    event.preventDefault();

​

    const data = new FormData(event.target);

​

    const value = Object.fromEntries(data.entries());

​

   value.topics = data.getAll("topics");

​

    console.log({ value });

  }

​

  const form = document.querySelector("form");

  form.addEventListener("submit", handleSubmit);

 <form>

    <label for="name">Name</label>

    <input type="text" name="name" id="name" />

​

    <label for="email">Email</label>

    <input type="email" name="email" id="email" />

​

   <p>

     <input type="checkbox" name="topics" id="javascript" value="javascript" />

     <label for="javascript">JavaScript</label>

​

     <input type="checkbox" name="topics" id="html" value="html" />

     <label for="html">HTML</label>

​

     <input type="checkbox" name="topics" id="css" value="css" />

     <label for="css">CSS</label>

   </p>

​

    <button type="submit">Submit</button>

  </form>