Develop Reference

Trying to check for empty value in input

I have an input box that changes another paragraph in my site with JavaScript. It works flawlessly, except for the fact that when I enter nothing in the input, it blanks out the paragraph.
I don't want this to happen. I've tried almost every piece of code I've found online to fix this issue but nothing has worked.
<div class="tasklist">
<p id="task1" style="color:#d3d3a3">You don't have any tasks.</p>
</div><br>
<script>
const element = document.getElementById("task1");
var task = document.input["task"].value;
function getInputValue() {
let value = document.getElementById("task").value;
element.innerHTML = (value);
document.getElementById("task1").style.color = "white";
}
</script>
Enter a task:<br>
<input type="text" id="task" name="task" placeholder="Pay Bills">
<button onclick="getInputValue();" onclick="changeColor()">+ Add</button>

<div id="tasklist">
<p id="msg" style="color:red">You don't have any tasks.</p>
</div>
<br>
<script>
const element = document.getElementById("msg");
element.style.display = "none";
function add() {
let value = document.getElementById("task").value;
if (value && value.trim() != "") {
document.getElementById("task").value = "";
element.style.display = "none";
const taskContainer = document.getElementById('tasklist');
const task = document.createElement('p');
task.textContent = value;
taskContainer.append(task)
} else {
element.style.display = "block";
}
}
</script>
Enter a task:<br>
<input type="text" id="task" name="task" placeholder="Pay Bills">
<button onclick="add();">+ Add</button>

First of all add value checker - it will prevent from setting innerHTML as "".
Secondly i think You want to add element with another task, not removing older ones.
use .append() to add at the end of parent or prepend() to add at the begginning of parrent.
<div class="tasklist"><p id="task1" style="color:#d3d3a3">You don't have any tasks.</p></div><br>
<script>
const element = document.getElementById("task1");
var task = document.input["task"].value;
function changeColor(){console.log("color")};
function getInputValue() {
let value = document.getElementById("task").value;
if(value.length>0){
element.append(
Object.assign(
document.createElement("p"),
{textContent:value}
)
);
document.getElementById("task1").style.color = "white";}}
</script>
Enter a task:<br>
<input type="text" id="task" name="task" placeholder="Pay Bills">
<button onclick="getInputValue();changeColor()" >+ Add</button>
if You rather want to replace Your first child then
<div class="tasklist"><p id="task1" style="color:#d3d3a3">You don't have any tasks.</p></div><br>
<script>
const element = document.getElementById("task1");
var task = document.input["task"].value;
function getInputValue() {
let value = document.getElementById("task").value;
if(value.length>0){
element.replaceChild(Object.assign(document.createElement("p"),{textContent:value}),element.firstChild);
document.getElementById("task1").style.color = "white";}}
</script>
Enter a task:<br>
<input type="text" id="task" name="task" placeholder="Pay Bills">
<button onclick="getInputValue()" >+ Add</button>

html javascript form no longer working since adding new input field

I have the following html and javascript code for validation on the input fields, this was working with the one input field for first name but since I tried to extend my code by adding a new input field for last name now the form validation has stopped working as follows:
function myFunction() {
let x = document.getElementsByName("first_name").[0]value;
let y = document.getElementsByName("last_name")[0].value;
let text;
text = "";
if (x == '' || x == null) {
text = "Input not valid";
}
document.getElementById("first_name_errors").innerHTML = text;
}
if (y == '' || y == null) {
text = "Input not valid";
}
document.getElementById("last_name_errors").innerHTML = text;
}
document.addEventListener('invalid', (function () {
return function (e) {
e.preventDefault();
document.getElementsByName("first_name").focus();
document.getElementsByName("last_name").focus();
};
})(), true);
</head>
<body>
<input type="text" name="first_name" placeholder="first name" name class="input_fields" required>
<div class="error-message" id="first_name_errors"></div>
<input class="save_btn" type="submit" value="Save" name="save_fname" onclick="myFunction()">
<br><br>
<input type="text" name="last_name" placeholder="last name" name class="input_fields" required>
<div class="error-message" id="last_name_errors"></div>
<input class="save_btn" type="submit" value="Save" name="save_lname" onclick="myFunction()">
How can I get this back working with the extra input field last name added? Thanks in advance

there are many errors here. you may find them by your own by debugging your console.log
error, at let x = document.getElementsByName("first_name").[0]value;
there are a to many }
eventlisteners need to be on the input and shouldn't be inside the check function
there are empty name attributes on your inputs
fixing it blind it would be something like:
let firstName = document.getElementsByName('first_name')[0];
let lastName = document.getElementsByName('last_name')[0];
function checkValid() {
let x = firstName.value;
let y = lastName.value;
let text;
text = '';
if (x == '' || x == null) {
text = 'Input not valid';
}
document.getElementById('first_name_errors').innerHTML = text;
if (y == '' || y == null) {
text = 'Input not valid';
}
document.getElementById('last_name_errors').innerHTML = text;
}
firstName.addEventListener('invalid', function () {
firstName.focus();
});
lastName.addEventListener('invalid', function () {
lastName.focus();
});
<input type="text" name="first_name" placeholder="first name" class="input_fields" required>
<div class="error-message" id="first_name_errors"></div>
<input class="save_btn" type="submit" value="Save" name="save_fname" onclick="checkValid()">
<br><br>
<input type="text" name="last_name" placeholder="last name" class="input_fields" required>
<div class="error-message" id="last_name_errors"></div>
<input class="save_btn" type="submit" value="Save" name="save_lname" onclick="checkValid()">

Populate a dropdown with previous user input

I have a text input where user have to enter their surname and I want that surname as they enter it to appear below in a dropdown, using HTML and Javascript. This is my code so far but it does not work:
<form id= 'surnameReg'>
<label for='surname'>Surname:</label>
<input type='text' id="surname">
</form>
<form id='chooseSur'>
<label for="who">Who:</label>
<select id="who">
</select>
</form>
And my JS:
function drop() {
var surnArr=[];
var select = document.getElementById("who");
for(var i = 0; i <surnArr.length; i++) {
var sur= surnArr[i];
var op = document.createElement("option");
op.textContent = sur;
op.value = sur;
select.appendChild(op);
}
}

You can set an event listener on the first form on submit and then create and append the option as follows:
document.getElementById("surnameReg").addEventListener("submit",function(e){
e.preventDefault();
let surname = document.getElementById("surname").value;
if(surname){
var select = document.getElementById("who");
var op = document.createElement("option");
op.textContent = surname;
op.value = surname;
select.appendChild(op);
}
});
<form id= 'surnameReg' >
<label for='surname'>Surname:</label>
<input type='text' id="surname" >
</form>
<form id='chooseSur' >
<label for="who">Who:</label>
<select id="who">
</select>
</form>

how to show user input in the body when a button is clicked

I'm trying to display a user input on a separate div, but only have it appear when a button is clicked. I think i have it set up but I'm just not sure how to display the input. can someone help me with how it can be done?
<script>
var callButt = document.getElementById("callButt");
var userinput = document.getElementById("userinput");
callButt.addEventListener("click", function(){
console.log("Call has been set");
userinput.style.display = "block";
</script>
<input id="callerIDInput" type="text" value="" >
<div id="userinput"> </div>
<button id='callButt'>CALL</button>

Set the input value to the innerHTML of the div
var callButt = document.getElementById("callButt");
var userinput = document.getElementById("userinput");
callButt.addEventListener("click", function() {
console.log("Call has been set");
userinput.innerHTML = document.getElementById('callerIDInput').value
})
<input id="callerIDInput" type="text" value="">
<div id="userinput"> </div>
<button id='callButt'>CALL</button>

Use innerHTML of the DIV to set the value.
HTML
<input id="callerIDInput" type="text" value="">
<div id="userinput"> </div>
<button id='callButt' onclick="Display()">CALL</button>
Javascript
function Display()
{
var callButt = document.getElementById("callButt");
var userinput = document.getElementById("userinput");
var callerIDInput = document.getElementById("callerIDInput");
console.log("Call has been set");
userinput.style.display = "block";
userinput.innerHTML = callerIDInput.value;
}

Using a checkbox to show entered values in a field to another field when a check box is clicked

Html - Delivery address has to give the entered value to billing address. The javascript and html are in separate files
Other js features are working fine, but its just this one that doesn't seem to work
<div class="textinput">
<label for="deladdress">Delivery Address: </label>
<input id="deladdress" type="text" name="Delivery Address" />
</div>
<div id="buttoncheckarea">
<input id="CheckDelivery" type="checkbox" name="CheckDelivery">
<label id="diff" for="CheckDelivery">Same as delivery address?</label>
</div>
<div class="textinput">
<label for="postcode">Postcode: </label>
<input id="postcode" type="text" name="postcode" />
</div>
<div class="textinput">
<label for="billaddress">Billing Address: </label>
<input id="billaddress" type="text" name="Billing Address" />
</div>
javascript
function deliveryfunc() {
var delivery = document.getElementById("deladdress").value;
var billing = document.getElementById("billaddress").value;
//var checkbox = document.getElementById("CheckDelivery").checked;
if (document.getElementsByName("CheckDelivery").checked == true) {
billing = delivery;
}
}
function init () {
var order = document.getElementById("ordForm");
order.onsubmit = ordervalidation;
order.onclick = radiobuttoncheck;
var checkbutton = document.getElementsByName("CheckDelivery");
checkbutton.onclick = deliveryfunc;
}
window.onload = init;

Try updating your deliveryfunc as below:
function deliveryfunc() {
var delivery = document.getElementById("deladdress");
var billing = document.getElementById("billaddress");
if (document.getElementById("CheckDelivery").checked == true) {
billing.value = delivery.value;
}
}
function init () {
var order = document.getElementById("ordForm");
order.onsubmit = ordervalidation;
order.onclick = radiobuttoncheck;
var checkbutton = document.getElementById("CheckDelivery");
checkbutton.onclick = deliveryfunc;
}
window.onload = init;