JSFiddle - React, Tailwind, and code Playground

HTML

<h3 class="check_num_char">15 символов :-)</h3>
<h3 class="check_num_char">16 символов :-))</h3>
<h3 class="check_num_char">14 символов :)</h3>
<h3 class="check_num_char">13 символов )</h3>

CSS

.red {
  background: red;
  color: white;
}

JavaScript

$('.check_num_char').each(function(){
		var $this = $(this);
		if ( $this.text().length >= 15 ) {
    		$this.addClass('red');
    }
});