script.js

const inputbox=document.getElementById("input-box");
const listcontainer=document.getElementById("list-container");
const inputbox1=document.querySelector("#input-box");
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();
}

inputbox1.addEventListener("keyup", (event) => {
      if(event.keyCode === 13) {
          addtask();
      }
  })

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