在bootstrap 4中需要动态行

<div class="row">
  <div class="col-4">Column 1</div>
  <div class="col-4">Column 2</div>
  <div class="col-4">Column 3</div>
</div>

<div class="d-flex">
  <div class="flex-fill">Column 1</div>
  <div class="flex-fill">Column 2</div>
  <div class="flex-fill">Column 3</div>
</div>

<div id="container"></div>

<script>
  var container = document.getElementById("container");
  
  for (var i = 0; i < 3; i++) {
    var column = document.createElement("div");
    column.className = "col-4";
    column.textContent = "Column " + (i+1);
    
    container.appendChild(column);
  }
</script>