Question

我有两个选择框。仅更新第二个选择。如果我删除ff.add tf.add有效。

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function copyToFrame(selectedOption) {

  if (selectedOption == "New") {
    var tf = document.getElementById("sCopyToFrame");
    var option = document.createElement("option");

    document.getElementById('copyToFrameCounter').value = parseInt(document.getElementById('copyToFrameCounter').value) + 1;
    option.text = "Frame " + document.getElementById('copyToFrameCounter').value;
    tf.add(option);

    var ff = document.getElementById("sCopyFromFrame");
    ff.add(option);
  }
}

＆＃13;

<INPUT type="hidden" id="copyToFrameCounter" value="0">
<p> Copy to frame:
  <select id="sCopyToFrame" onchange="copyToFrame(this.value);">
        <option selected disabled hidden style='display: none' value=''></option>
        <option>New</option>
      </select>
</p>
<p> Copy from frame:
  <select id="sCopyFromFrame">
        <option selected disabled hidden style='display: none' value=''></option>
        <option></option>
      </select>
</p>

＆＃13;

Answer 1

＆＃13;

a) Handler
b) Alarm Manager
c) JobScheduler
d) Firebase JobDispatcher
e) SyncAdapter
f) ..anything else if there is...

＆＃13;

function copyToFrame(selectedOption) {

  if (selectedOption == "New") {
    var tf = document.getElementById("sCopyToFrame");
    var ff = document.getElementById("sCopyFromFrame");
    var option = document.createElement("option");
    var optionCopy = document.createElement("option");
    var cTFC = parseInt(document.getElementById('copyToFrameCounter').value) + 1 || 0;

    option.text = "Frame " + cTFC;
    optionCopy.text = "Frame " + cTFC;
    
    tf.add(option);
    ff.add(optionCopy);
  }
}

＆＃13;

Answer 2

如果要为两个下拉列表添加新选项，则需要两个元素

function copyToFrame(selectedOption){

    if(selectedOption == "New"){
        var tf = document.getElementById("sCopyToFrame");
        var tf_option = document.createElement("option");

        document.getElementById('copyToFrameCounter').value = parseInt(document.getElementById('copyToFrameCounter').value) + 1;
        tf_option.text = "Frame " + document.getElementById('copyToFrameCounter').value;
        tf.add(tf_option);

        var ff = document.getElementById("sCopyFromFrame");
        var ff_option = tf_option.cloneNode(true);
        ff.add(ff_option); 
  }
}

更新具有相同信息的两个选择框

2 个答案: