如何在JavaScript中每个会话显示一次更改事件的事件警报弹出窗口一次

Question

我有一个下拉值列表，应在JavaScript中每次会话一次提醒弹出窗口。在更改中，如何在下拉列表中提醒任何值，但应适用于一个选择值(下拉(。我试图提醒。请建议如何使用JavaScript中的会话存储来实现它。

jQuery("#dim_height").on('focus', function() {
  // Store the current value on focus and on change
  previous = this.value;
}).change(function() {
  var r1 = confirm("Are you sure want to change the template?");
  if (r1 == true) {
    calci_width();
  } else {
    jQuery(this).val(previous);
    return;
  }
  //reset_template(previous);	
  //calci_width();	
});
jQuery("#dim_width").on('focus', function() {
  // Store the current value on focus and on change
  previous = this.value;
}).change(function() {
  var r = confirm("Are you sure want to change the template?");
  // console.log(r);
  if (r == true) {
    calci_width();
  } else {
    jQuery(this).val(previous);
    return;
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="dim_width" id="dim_width" class="drop">
  <option value="8">8</option>
  <option value="12">12</option>
  <option value="18">18</option>
  <option value="24">24</option>
  <option value="36">36</option>
  <!-- <option value="48">48</option>
  <option value="72">72</option>
  <option value="84">84</option>
  <option value="96">96</option> -->
</select>
<select name="dim_height" id="dim_height" class="drop">									
  <option value="8">8</option>
  <option value="12">12</option>
  <option value="18">18</option>
  <option value="24">24</option>
  <!-- <option value="36">36</option>
  <option value="48">48</option> -->
</select>

Answer 1

这是一个示例，说明如何使用cookie每次会话一次提醒：

<script 
src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"> 
</script><!-- notice jquery version change-->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery- 
cookie/1.4.1/jquery.cookie.min.js"></script><!-- added cookie plugin-->
<select name="dim_width" id="dim_width" class="drop">
    <option value="8">8</option>
    <option value="12">12</option>
    <option value="18">18</option>
    <option value="24">24</option>
    <option value="36">36</option>
</select>

然后使用jQuery：

$('#dim_width').on('change', function(){
     if (typeof $.cookie('alerted') === 'undefined'){//does cookie exist?
         var Selected = $('#dim_width').val();
         alert(Selected); //if not alert value
         $.cookie("alerted", 1); //then set cookie, will expire one browser closes 
      }
 })

小提琴：https：//jsfiddle.net/9wxwfs4c/2/