check for duplicate before appendChild

December 24, 2021

const pickNewUl = document.getElementById("ullist1");     
var createLi = document.createElement("li");
                            createLi.id = listItems[i].id;
                            createLi.classList.add(pickNewUlsl);
                            createLi.innerHTML = listItems[i].textContent; 
                            createLi.innerHTML += "<a onclick='remove(this)' class='removebtn'>X</a>";
pickNewUl.appendChild(createLi);

What I need to check in above code is: I want to check if there are any same id LI exists or not, if not then only it should append, otherwise it will not append.

pickNewUl is a UL list

>Solution :

You can find for any element inside element with .querySelectorAll as below.

if (pickNewUl.querySelectorAll('#' + listItems[i].id).length === 0) {
    // Add element    
}

Reference : https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelectorAll

Your complete code should be like below.

const pickNewUl = document.getElementById("ullist1"); 
if (pickNewUl.querySelectorAll('#' + listItems[i].id).length === 0) {   
    var createLi = document.createElement("li");
    createLi.id = listItems[i].id;
    createLi.classList.add(pickNewUlsl);
    createLi.innerHTML = listItems[i].textContent; 
    createLi.innerHTML += "<a onclick='remove(this)' class='removebtn'>X</a>";
    pickNewUl.appendChild(createLi);
}