How can I create a filter for unavailable urls? (javascript)

Question

Hello, I was wondering how I can filter certain sub-domains that would simulate my company’s brand for example: in a free hosting the user types a Sub-domain to the address of his website. if he typed a domain as just the word "blog" or "forum", "news". a notice would appear stating that this domain is invalid. i would like a client-side script, and only to avoid that users create sites simulating my company’s brand as for example: he could not create blog.meudominio.xy, filter these words, but when typed "blog21.meudominio.xy" do not appear this warning.

Answer 1

You can create an array on js and use the method indexOf. Ex:

const subdomainDisabled = ["blog", "news", "cdn"];
const input = document.querySelector("input");
const btn = document.querySelector("button");

btn.addEventListener("click", function() {
  if (subdomainDisabled.indexOf(input.value) >= 0) {
    alert("Choose another subdomain");
    input.value = "";
  } else {
    $('#ID-DO-MODAL').modal("show");
  }
});

<input type="text" id="subdomain" />
<button type="button">Register</button>