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 showTask() {
    listContainer.innerHTML = localStorage.getItem("data");
}
showTask();