How to block Cyrillic unicode by jQuery on form submit

Question

In my website, I'm receiving some subscriptions spam. All of them is from people which type their names using Russian alphabet.

I know that in this case the most recommended thing to do is put a captcha in my subscription page form. But, as this case is so specific, and at the same time I don't want to affect my real customers experience, in a first time I would like to have a jQuery script which deny the form submit when detects Russian alphabet in some input. Can some one help me with it? (Or is better do it using PHP?)

Simple form exemple

<form action="#" id="form-validate">
  <input type="text" class="input" id="firstname">
  <button class="submit">teste</button>
</form>  

To be more specific. For example, a script that detects a Cyrillic character in the input string, such as: "John Потоцкая Doe", and then avoid the form submit.

Thanks a lot in advance.

Answer 1

I'd use a Regex range that hits all the Cyrillic unicode ranges:

let pattern  /[\u0400-\u04FF]/;
if (pattern.test("John Потоцкая Doe")) console.log("cyrillic");
else console.log("not cyrillic");

^{Relevant SO Question}

Your code will end up looking like this:

let pattern = /[\u0400-\u04FF]/;

$(document).ready(function() {
  $('#form-validate').submit(function() {
    if (pattern.test($('input#firstname').val())) { //If "input" contains a Cyrillic character...
      alert('Invalid input: please use Latin characters only.'); // pop alert message
      $('input#firstname').val("") // empty field of invalid contents
      return false; // prevent form from submitting
    } else
      return true; // allow form to be submitted
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="#" id="form-validate">
  <input type="text" class="input" id="firstname">
  <button class="submit">teste</button>
</form>

Answer 2

You could see where Cyrillic characters live in the Unicode space here:

https://en.wikipedia.org/wiki/Cyrillic_script_in_Unicode

Then loop through character by character to see if any character falls in that range, something like:

let str = 'Україна';
let cyrillic = false;
for (let i = 0; i < str.length; i++) {
  if (str.codePointAt(i) >= 0x0400 && str.codePointAt(i) <= 0x052f) {
    cyrillic = true;
  }
}

There may be an easier way with regexes, e.g. range /[A-Za-z]/ gives Latin letters, may be something similar for general Unicode code points.

Edit

This might be slightly cleaner with ES5 Array prototype methods, e.g. one-liner would be:

let cyrillic = str.split('').some(char => char.codePointAt(0) >= 0x0400 && char.codePointAt(0) <= 0x052f);