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("chcked");
            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();