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How to create input tag with js without it being ":valid" for css purpose

I have super simple input witch I have written in html/css and it works as it should but when I decided to write function in js to automate process of creating multiple inputs I had a problem. Input that I created with js is already valid(from css ":valid" standpoint) and it is not when i write it in just html/css. I need it to be invalid from the start when it doses not have any content in it and then when i write something in it, it needs to become valid. Here is CodePen with the code. So to sum up I need to know how to make js version same as html/css version.
I have tried both .setCustomValidity(0) and .value = '' the problem with first is that input stays :invalid even when I type something in to the input. Second solution dose not work at all.

The HTML input is invalid because it is required (and empty).
The example JavaScript code does not set the required attribute on the input.
const input = document.createElement('input')
input.required = true;
document.body.appendChild(input);
console.log(document.querySelector(':invalid'));
Please don’t forget to provide a real <label> for the input. It’s very important to make the form accessible with assistive technology for users with disabilities.
What is currently named placeholder is actually a label. Material Design calls it a floating label, because it will be floating above the input once it has a value.
const placeholder = document.createElement('label');
…
input.id = 'theinput';
placeholder.setAttribute('for', 'theinput');

How to restrict from entering a decimal value in input type number?

So I want to have an input of type number <input type="number"> and I want to RESTRICT users from ENTERING DECIMAL VALUE
Note: I'm hiding the spin buttons of the input type text. Know more here
EDIT: ANYTHING WILL WORK! EVEN JAVASCRIPT!
I searched a lot but found nothing.
I did find this answer but it basically blocks the use of any other key on the keypad except the number keys, so the basic problems occur such as the user cannot use backspace and cut the number entered, another problem is the user cannot use tab to change focus onto the next input.
Thank You!

Preventing user input can be done with JavaScript. I'd use the input event for catching values, as it's a unified interface, encompassing any input method you can think of keyup, paste, pointer events, touch events, etc...
document.querySelector('input').addEventListener('input', e => {
e.target.value = Math.round(e.target.value.replace(/\D/g,''))
});
<input>
But you really should not do it! For at least the following reasons:
Forbidding user input is, by and large, perceived as disrespectful and drives users away. In short, it reduces any user engagement metric you can think of (funneling, sales, visits, sharing, etc...). Don't take my word for it. Do some A/B testing: present the same form with and without blocking user input and look at the results.
Form elements are just tools to help users give you data. But they are completely by-pass-able. If you give me a form I can send whatever I want using it, by simply opening the browser console. The validation must be done on server side. If you're using the value to do something on client side, sanitize the input value in the method, without changing user input.
A respectful way to inform users decimal values are not valid is by making the input :invalid, using the pattern attribute ( e.g: pattern="[0-9]"), styling accordingly (e.g: :invalid { border-color: red }), and displaying an appropriate message.
Don't delete or block user input. They'll do it themselves if you tell them why the value is invalid.
When following web standards, your solution lasts. When you come up with hacks, there will always be the odd device in which your hack doesn't work. You don't know where things will be in 1-2 years from now, nevermind 5 or 10.
Last, but not least, have a closer look at Constraint Validation. You'll need to know and use it when creating quality UX and accessible forms.

This is one option for creating an input element using javascript to limit the values that can be entered. I create an array of allowed keys, including all the digits, backspace, and tab as you specified. I added an event listener for the keydown event, and if the key pressed is not in the allowed group, I prevent the default action, or prevent the value from being entered.
I also added an event listener to the paste event, as you could right click paste and enter information that does not meet the criteria. Instead of trying to validate pasted values I disable pasting all together.
If you have any questions, please ask.
const allowedKeys = [..."0123456789", "Backspace", "Tab"];
const myInput = document.querySelector("input");
myInput.addEventListener("keydown", e => {
const key = e.key;
const allowed = allowedKeys.includes(key);
if (!allowed) e.preventDefault();
});
myInput.addEventListener("paste", e => e.preventDefault());
<input type="number">

Simulate sending data to the text input field with JS

I have a task where I need to automate Sign in form authentication. For this example, I'll show you Tiktok authentication form (Mobile interface, not desktop. E-mail and password option)
If I enter text values into the fields programmatically, the Login button won't become active, and if I manually focus on the fields with a mouse click, the value disappears. These are two lines of code I run to put the value in:
let email_input = document.getElementsByName("email")[0];
email_input.value = 'sample#email.com';
I understand it needs to trigger a certain event to assign a value into it's JS model, but I can't figure out how to do it. I have tried sending change or input events onto this text field with no luck using this code:
let email_input = document.getElementsByName("email");
email_input[0].value = 'sample#email.com';
custom_event = new Event('input');
email_input[0].dispatchEvent(custom_event);
// tried also change, textInput like so:
custom_event = new Event('change');
email_input[0].dispatchEvent(custom_event);
But this does not seem to help.
So my goal is to put values into both fields Email and Password in the way it will be detected and Log in button would become active.
Any suggestion would be much appreciated

You should first focus needed input element and then execute document.execCommand with insertText command:
let email_input = document.getElementsByName("email");
email_input[0].focus();
document.execCommand('insertText', false, 'sample#email.com');
With this method input\textarea value modification should be captured by all major frameworks including Angular and Vuejs. This modification will be processed by frameworks the same way as if user pressed "Paste" option in browser main menu.

It all depends...
Who/what are you? A normal browser user? A bot? The browser author?
Because code like this is useless...
let email_input = document.getElementsByName("email")[0];
What document are you referring to? Who's document? Did you inject this instruction into the page and executed it?
You're not telling us where you're coming from, but anyway...
If you are the browser author, or you can run JavaScript macros from your browser (ie: the Classic browser) then you can do something like this...
var Z=W.contentWindow.document.querySelectorAll('input[type="password"]');
if(Z.length>0){
Z[0].value='password123';
Z=W.contentWindow.document.querySelectorAll('input[type="email"]');
if(Z.length>0){Z[0].value='email#abc.com';}
}
To automatically populate such fields, and if you also want you can SubmitButtonID.click() the submit button for as long as the isTrusted property is not tested by the website.

Continued...
Test if normal (non-custom) submit button exists and click...
Z=W.contentWindow.document.querySelectorAll('input[type="submit"]');
if(Z.length>0){
if(Z[0].hasAttribute('disabled')){Z[0].removeAttribute('disabled');} <--- Enable it if disabled
Z[0].click(); <--- automate click
}

Pre-loading text in textarea for user to edit and submit shows text briefly then blanks out. Why?

I'm writing an edit function (plain javascript & HTML / Chrome / Windows 10).
The data is in localStorage as a series of records, just 2 records in the toy code mentioned below.
I want the user to specify the number of the record to edit, then the code should pre-fill the textarea field with the retrieved content of that record. I want to allow the user to make changes and then press a Store button to store it back in localStorage.
My problem is that when I prefill the input field, I see the record content briefly and then the input field clears. I've tried .value and .defaultValue
editField.value = localStorage.getItem('jnl' + locStoreNo).replace(/(.*?) `\d*?`/, "$1");
and
editField.defaultValue = localStorage.getItem('jnl' + locStoreNo).replace(/(.*?) `\d*?`/, "$1");
the result is the same. (The regex is to hide a sequence number)
The code is in a JSFiddle here: https://jsfiddle.net/roygrubb/zxedbfqr/2/
That performs more or less the same - it shows the value briefly - but then does something different: It goes to a 404. I don't understand this either ¯_(ツ)_/¯
What I'm trying to do seems so basic, that I think I must be missing something blindingly obvious.
What have I missed? Thanks!

Whenever you've got a <form> that you want to handle through JavaScript, you have to ensure that the default form submission action does not happen. If the <form> does not have an "action" attribute, the default is to reload the current page.
By default, a <button> element will be assumed to have "submit" as its type. To prevent form submission, therefore, the simplest thing to do is make the button have "button" as its type.
That may not be all you need to do, depending on the details of the form. It may be necessary (or simply a good defensive move) to have a handler for the "submit" event on the form to prevent the default action.

jQuery onClick once with on/off switch

I am trying to figure out how to do something but can not figure out the correct terminology to do so.
What I am trying to do is have a textbox (#price) that when clicked once it will open up a pdf calculator that will then either prefill the textbox when completed or will then allow the user to enter the amount in. But I also want this to work if the textbox is "tabbed" over to also instead of the onClick. (Maybe onBlur) Basically anytime that textbox is used I need it to work like that. But how do I make the onClick know when the amount is ok to be entered or if the calculator needs to open?
What also makes this tricky is I need to have an On/Off switch basically a checkbox that when checked it allows that pop up pdf calculator and when its not checked it just ignores it and allows the price to be entered still.
Does anyone have any suggestions or pointers in how I can achieve this goal?

1. A textbox (#price) that when click once it will open up a pdf calculator
Use jQuery's click() handler or bind("click", ...)
var $price = $("#price");
$price.click(function() {
$("#pdf_calculator").fadeIn();
});
2. But I also want this to work if the textbox is "tabbed" over to also
Use the focus event to know when an input is active (i.e, has been "tabbed" to). Alternatively, the blur event can be used if you want to know when a user is "leaving" the input field. ('blur' is the opposite of 'focus')
$price.on("focus click", function() {
$("#pdf_calculator").fadeIn();
});
3. But how do I make the onClick know when the amount is ok to be entered or if the calculator needs to open?
Grab the amount typed in by the user, convert it to a numerical value, then perform your validation steps.
$price.on("focus click", function() {
// Do some validation checking on the amount entered.
var enteredValue = parseFloat($price.val());
if (!isNaN(enteredValue) && enteredValue > 0) {
$("#pdf_calculator").fadeIn();
}
});
4. What also makes this tricky is I need to have an On/Off switch basically a checkbox that when checked it allows that pop up pdf calculator and when its not checked it just ignores it and allows the price to be entered still.
Simply check that the checkbox is checked using jQuery's is(":checked") then combine the steps above, and your fully working code looks like this:
var $price = $("#price");
$price.on("focus click blur", function() {
// your checkbox element
var checkbox = $("#show_calculator");
// Check if the checkbox is checked
if (checkbox.is(":checked")) {
// convert the entered string to a number
// then validate it according to your needs
var enteredValue = parseFloat($price.val());
if (!isNaN(enteredValue) && enteredValue > 0) {
// if all conditions are met,
// show the pdf calculator
$("#pdf_calculator").fadeIn();
}
}
});
Click here to review a working jsfiddle of these ideas.
As for the pdf form (and getting values in and out again of a pdf form) there isn't a straight-forward method that doesn't involve a 'hack' (that may or may not work across different browsers). If the pdf only has ONE input, then you can capture the keyboard events on your form popup, and send them back to the HTML form (which is an ugly hack), but if this were my project, I would just convert the pdf functionality to javascript, and then you have all the freedom you need, and your calculator is 100% compatible with the rest of your application.
Hope this helps!

The event(s) you are looking for is onFocus and onBlur. I would bind a function to the onFocus event that first checks if the corresponding checkbox has a "true" (or "checked") value, then continue if it does and do nothin if it doesn't.
I'd create an example in jsfiddle for you if I wasn't answering this from my phone.

Bind event handler to focus event (blur is for when control looses focus).
$("#price").on({
"focus": eventHandler
})
Then in your eventHandler() check if calculator needs to be invoked, by checking if it's already opened: $("#calculatorDiv").is(":visible"), and checking if your checkbox is 'checked': $("#checkboxId").is(':checked'), and depending on that open it.