JavaScript to implement drop-down list selection box

JavaScript to implement drop-down list selection box

This article example shares the specific code of JavaScript to implement the drop-down list selection box for your reference. The specific content is as follows

Create a page

** Two drop-down selection boxes
- Set the attribute multiple attribute - multiple = "multiple" (the drop-down selection box displays multiple lines)
** Four buttons with events

Tip: Select multiple options by holding down ctrl or shift and clicking on them.

The code is as follows:

<html>
 <head>
   
  <title>HTML Example</title>
  <style type = "text/css">
  div#left{
 float:left;
  }
 
  </style>
 </head>
 <body>
 <div id="left" ">
  <div >
    <select id="select1" multiple="multiple" style="width:100px;height:1ss00px">
   <option>AAAAAA</option>
   <option>BBBBBB</option>
   <option>CCCCCC</option>
   <option>DDDDDD</option>
   <option>EEEEEE</option>
    </select><br/>
    </div>
 
    <div>
    <input type="button" value="Select and add to the right" onclick="selToRight()"/><br/>
    <input type="button" value="Add all to the right" onclick="selAllRight()"/>
    </div>
   </div>
 
 <div id="right">
    <div >
    <select id="select2" multiple="multiple" style="width:100px;height:1ss00p">
  <option>FFFFFF</option>
    </select><br/>
    </div>
 
    <div>
    <input type="button" value="Select and add to the left" onclick="selToLeft()"/><br/>
    <input type="button" value="Add all to the left" onclick="selAllLeft()"/>
    </div>
 </div>
 
 </body>
 <script type="text/javascript">
//Select and add to the left function selToLeft(){
 //Get the select object on the left var s1 = document.getElementById("select1");
  //Get the select object on the right var s2 = document.getElementById("select2");
  //Get each option in the select object on the left
  var ops = s2.getElementsByTagName("option");
  for(var i4=0;i4<ops.length;i4++){
   op4=ops[i4];
   if(op4.selected==true){
   s1.appendChild(op4);
   i4--;
   }
  }
}
 
 //Add all to the left function selAllLeft(){
  //Get the select object on the left var s1 = document.getElementById("select1");
  //Get the select object on the right var s2 = document.getElementById("select2");
  //Get each option in the select object on the left
  var ops = s2.getElementsByTagName("option");
  for(var i3=0;i3<ops.length;i3++){
   op3=ops[i3];
   s1.appendChild(op3);
   i3--;
  }
 }
 //Add all to the right function selAllRight(){
  //Get the select object on the left var s1 = document.getElementById("select1");
  //Get the select object on the right var s2 = document.getElementById("select2");
  //Get each option in the select object on the left
  var ops = s1.getElementsByTagName("option");
  for(var i2=0;i2<ops.length;i2++){
   op2=ops[i2];
   s2.appendChild(op2);
   i2--;
  }
 }
  //Select and add to the right function selToRight(){
  /*
   step:
   1. Get the option in the select
    -getElementByTagName() - returns an array - traverses the array and gets each option
   2. Determine whether option is selected - attribute selected, determine whether it is selected - selected = true; selected - selected = false; unselected 3. If selected, add the selected one to the right 4. Get select2
   5. Add the selected part - appendChild() method*/
  //Get the select object on the left var s1 = document.getElementById("select1");
  //Get the select object on the right var s2 = document.getElementById("select2");
  //Get each option in the select object on the left
  var ops = s1.getElementsByTagName("option");
  //Traverse the ops array to get the selected state of each option for(var i1=0;i1<ops.length;i1++){
   op1 = ops[i1];
   // Determine whether the selected attribute in each option is selected if (op1.selected == true) {
    //If selected, add to the select on the right //-Use appendChild() method s2.appendChild(op1);
    //Each addition will reduce the length of the array by one. After i1++, the length becomes abnormal, so we need to --;
    i1--;
   }
  }
 }
 
   </script>
 
</html>

Effect picture:

The above is the full content of this article. I hope it will be helpful for everyone’s study. I also hope that everyone will support 123WORDPRESS.COM.

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