JSFiddle - React, Tailwind, and code Playground

HTML

<input type='text' name='tovar[]' data-uniqu-group="first"/>
<input type='text' name='tovar[]' data-uniqu-group="first"/>
<input type='text' name='tovar[]' data-uniqu-group="first"/>

CSS

input{
  display:block;
}
.invalid{
  border:solid 1px red;
}

JavaScript

$('[data-uniqu-group]').on('input',function(){
	var $this=$(this).removeClass('invalid');
 	$('[data-uniqu-group="'+$this.data('uniqu-group')+'"]').each(function(){
  	if(this!==$this.get(0) && this.value==$this.val())
    	$this.addClass('invalid');
  });
});