main.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();