script.js

const inputbox = document.getElementById('input-box');
const listcontainer = document.getElementById('list-container');

function addTask() {
    if (inputbox.value === '') {
        alert("You must write something");
    }
    else {
        let li = document.createElement("li");
        li.innerHTML = inputbox.value;
        listcontainer.appendChild(li);
        let span = document.createElement("span");
        span.innerHTML = "\u00d7";
        li.appendChild(span);
    }
    inputbox.value = "";
    savedata();
}

listcontainer.addEventListener("click", function (e) {
    if (e.target.tagName === "LI") {
        e.target.classList.toggle("checked");
        savedata();
    }
    else if (e.target.tagName === "SPAN") {
        e.target.parentElement.remove();
        savedata();
    }
}, false);


function savedata() {
    localStorage.setItem("data", listcontainer.innerHTML);
}

function showlist() {
    listcontainer.innerHTML = localStorage.getItem("data");
}

showlist();