I have a problem in Javascript.I am adding new list items to the 'ul' elements and this list is empty at first and I do not want to add same values twice. When I write the if statement I get the exception because my list is empty so the result return null. How can I fix this this problem? Thank you in advance...
Html Codes
<input type="text" id="the-filter" placeholder="Search For..." />
<div class="list-container">
<ul id="myList"></ul>
<button id="button">Click</button>
Javascript Codes
let newlist = document.querySelector("#myList");
const li = document.getElementsByClassName('list-group-item');
const button = document.getElementById("button");
const button.addEventListener('click' , listName);
const input = document.getElementById("the-filter");
function listName()
const inputVal = input.value;
for (i = 0; i < li.length; i++) {
if ((li[i].innerHTML.toLocaleLowerCase().includes(inputVal) && inputVal!="") ||
(li[i].innerHTML.toUpperCase().includes(inputVal) && inputVal!="")) {
let newItem = document.createElement("li");
li[i].classList.add("list-group-item");
let textnode = document.createTextNode(li[i].innerHTML.toLocaleLowerCase());
newItem.appendChild(textnode);
if((newlist.children[0].innerHTML.toLocaleLowerCase().includes(inputVal))){
newlist.insertBefore(newItem, newlist.childNodes[0]);
}
}
}
}
If I understood the task correct, you need to add items to the list by button click.
If same item exists (case insensitive), then nothing happens.
const list = document.querySelector("#myList");
const button = document.getElementById("button");
button.addEventListener("click", listName);
const input = document.getElementById("the-filter");
function listName() {
const inputVal = input.value;
const [...lis] = document.getElementsByClassName("list-group-item");
const same = lis.find((el) => el.textContent.toLowerCase() === inputVal.toLowerCase());
if (same) {
return;
}
let newItem = document.createElement("li");
newItem.classList.add("list-group-item");
newItem.textContent = inputVal;
list.appendChild(newItem)
}<input type="text" id="the-filter" placeholder="Search For..." />
<div class="list-container">
<ul id="myList"></ul>
<button id="button">Click</button>
</div>You're on the right track with event listeners and element creation, but your original code didn't quite seem to match your stated goal.
Here's a solution you might find useful, with some explanatory comments:
// Identifies some DOM elements
const
input = document.getElementById("my-input"),
newList = document.getElementById("my-list"),
items = document.getElementsByClassName('list-group-item'),
button = document.getElementById("my-button");
// Focuses input, and calls addItem on button-click
input.focus();
button.addEventListener('click', addItem);
// Defines the listener function
function addItem(){
// Trims whitespace and sets string to lowerCase
const inputTrimmedLower = input.value.trim().toLocaleLowerCase();
// Clears and refocuses input
input.value = "";
input.focus();
// Ignores empty input
if (!inputTrimmedLower) { return; }
// Ignores value if a list item matches it
for (const li of items) {
const liTrimmedLower = li.textContent.trim().toLocaleLowerCase();
if (liTrimmedLower === inputTrimmedLower) {
console.log(`${inputTrimmedLower} is already listed`);
return;
}
}
// If we got this far, we want to add the new item
let newItem = document.createElement("li");
newItem.classList.add("list-group-item");
newItem.append(inputTrimmedLower); // Keeps lowerCase, as your original code
newList.prepend(newItem); // More modern method than `insertBefore()`
}<input id="my-input" />
<ul id="my-list"></ul>
<button id="my-button">Click</button>