那么，您可以在表单中创建一个具有所需值的输入节点，然后提交它。

<form>
      <input autofocus type="text" name="rnum" id="rnum" class="input-field" placeholder="Number of rows in a page">
</form>
<script type="text/javascript">
        document.getElementById('rnum')
        .addEventListener('keyup', function(event) {
               if (event.code === 'Enter') {
                  let child = document.createElement('input');
                  child.name = "searchBox";
                  child.value = window.location.search.toString();
                  event.preventDefault();
                  var form = document.querySelector('form');
                  form.appendChild(child);
                  form.submit()
               }
        });</script>

如果您正在寻找更新页面url附加一些值从表单输入

<script type="text/javascript">
        document.getElementById('rnum')
        .addEventListener('keyup', function(event) {
               event.preventDefault();
               if (event.code === 'Enter') {
                  let input = document.getElementById("rnum");
                  window.location.search += "&rnum=" +input.value;
               }
        });</script>

我想你在这部分有语法错误

if (event.code === 'Enter') {
 .append(window.location.search) 
                  .toString();// this is an error since we are not appending the string anywhere
                  event.preventDefault();
                  document.querySelector('form').submit();
               }