By passing 1 second you need to add 1 marker in the list (list-style-type: circle;).

setInterval(function(){ var block = document.querySelectorAll('li'); for(i=0; i < block.length; i++) { block[0].classList.add('active'); i++; if(i===6) { break; } }; },1000); 
 ul { margin: 50px auto; width: 250px; } li { list-style-type: none; } li.active { list-style-type: circle; } 
 <ul> <li>Первый</li> <li>Второй</li> <li>Третий</li> <li>Четвёртый</li> <li>Пятый</li> <li>Шестой</li> </ul>

    1 answer 1

    It turned out something like this:

     var block = document.querySelectorAll('li'); var intervalId; var counter = 0; intervalId = setInterval(function() { if (counter == block.length - 1) clearInterval(intervalId); block[counter].classList.add('active'); counter++; }, 1000); 
     ul { margin: 50px auto; width: 250px; } li { list-style-type: none; } li.active { list-style-type: circle; } 
     <ul> <li>Первый</li> <li>Второй</li> <li>Третий</li> <li>Четвёртый</li> <li>Пятый</li> <li>Шестой</li> </ul>

    That is, write the counter identifier in the variable. When the counter is not needed - turn it off via clearInterval