Как вернуть все элементы с querySelectorAll

document.querySelector(".btn-info").addEventListener("click", function(){ 
    let required = document.querySelectorAll(".required"); 
    let isAllFilled = true; 
   
    for (let i = 0; i < required.length; ++i) { 
        if (required[i].value.trim() == "") { 
            isAllFilled = false; 
            break; 
	} 
    } 
   
    if (!isAllFilled) 
        alert("please fill all the columns"); 
});

.required { 
  display:block; 
  padding-bottom:10x; 
}

<form id="fld"> 
  <input id="question1" class="required"> 
  <input id="question2" class="required"> 
  <input id="question3" class="required"> 
  <input id="question4" class="required"> 
  <input id="question5" class="required"> 
</form> 
 <button type="button" class="btn btn-info">Отправить отзыв</button>

document.querySelector(".btn-info").addEventListener("click", function() { 
  var required = document.querySelectorAll(".required:invalid"); 
  if (required.length) { 
    console.log("please fill all the columns"); 
  } 
 
});

.required { 
  display: block; 
  padding-bottom: 10x; 
}

<form id="fld"> 
  <input id="question1" required class="required"> 
  <input id="question2" required class="required"> 
  <input id="question3" required class="required"> 
  <input id="question4" required class="required"> 
  <input id="question5" required class="required"> 
</form> 
<button type="button" class="btn btn-info">Отправить отзыв</button>