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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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">