Checking If the user entered value is a valid website address/name?

Question

So I have an input element in HTML, that input element asks the user for his website's address/name.

Now here's the thing I accept the following address/name formats:

• https://example.com (.net, .org, etc.)
• http://example.com (.net, .org, etc.)
• www.example.com (.net, .org, etc.)
• http://www.example.com (.net, .org, etc.)
• https://www.example.com (.net, .org, etc.)
• example.com (.net, .org, etc.)

But If the user types a random string for example, abc123$ It would give an error "Please enter a valid website address/name".

What I tried so far,

const isValidURL = (str) => {
  var a = document.createElement("a");
  a.href = str;
  return a.host && a.host != window.location.host;
}

let isValid = isValidURL("https://example.com");

if (isValid == true) {
  // pass
} else if ...

Now, this code I found on an SO answer checks to see If it is a valid URL, i.e. contains http or https which is part of what I want. But after this in an else if statement I would also want to allow URLs that don't contain http or https but contain www. and then in another else if statement I would want to allow URLs that contain neither of those and just example.com (.net, .org, etc.), but THEN an else statement which tells the user "Please enter a valid website address/name".

But the problem is that I have no idea how I will do this, I would appreciate it if someone were to shed some light upon this.

Note: I do know that checking the URL on the backend is the best thing to do but sadly due to client requirements I need to use this client-side method of the bare-minimum sitename validation.

Edit: This is not a duplicate of other such questions because I am not just trying to validate the URLs, I am trying to validate all the possible domain name types valid on a web browser. See the examples I presented above, not all of them are valid URLs the ones that aren't should pass too, but If it is not a valid site name entirely like "example" instead of "example.com, www.example.com, or http://example.com, etc." then It doesn't pass.