JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" size="10" onblur ="foo(this)">
<span id="help"></span>

JavaScript

function foo(inputField){
	var minln = 3;
  var maxl = 15;
	var bb = document.getElementById("help");
  if(inputField.value.length == 0){
 	  if(inputField.value.length > minln ){
    	 bb.innerHTML = "Заполнено";
    }
    	bb.innerHTML = "Заполните поле";
    }
	else if(inputField.value.length <=minln){
    	bb.innerHTML = "Минимум 4 символа";
  }
  else if(inputField.value.length > maxl) {
  	 bb.innerHTML = "Не более 15 символов";
  }
  else if(inputField.value.length != null){
      bb.innerHTML = "";
    }
    
  }