从下拉列表中选择选项后如何创建文本框？

Question

I'm trying to create a drop-down list with four options such that if I select the 4th option, I want a text box created so that I can get the value typed in that box using "$_GET"

Something like this;

<select name="value">
<option value="value1">Option 1</option>
<option value="value2">Option 2</option>
<option value="value3">Option 3</option>
<!-- And a 4th one -->
</select>

And if the 4th one is selected, a box should appear like this;

<input type="text" name="firstname">

---

Edit;

My current code;

<script>
jQuery(function($){                      //calling the code inside braces when document loads and passing jQuery object as '$' parameter;
   $("select[name='sortby']").change(function(){        //binding an event that fires every time select value changes
      var select = $(this);              //caching select, which value was changed
      if(select.val() === "byDefindex"){     //checking if we selected the right option
          $("<input>").attr({type: "text", name: "defindex"}).appendTo(select.parent());   //creating new input element object, setting its value to "value4" and appending to select parent element or wherever you want it
      }
   });        
});
</script>




<form action="<?php $_PHP_SELF ?>" method="GET">

    Select:
    <br />
        <select name="sortby">
            <option value="playHours">Play Hours</option>
            <option value="lastLogin">Last Login</option>
            <option value="byDefindex">By Defindex</option>
        </select>
    <br />

    <input type="submit" />

</form>

Answer 1

If your 4th option is this:

<option value="value4">Option 4</option>

You can use jQuery to display the field. Put your field in a <div>

<div id="field"><input type="text" name="firstname"></div>

Now,

<script type="text/javascript">
$(document).ready(function(){

$('input[name="value"]').change(function(){
var v = $('input[name="value"]').val();
if(v=="value4") $('#field').show();
else $('#field').hide();
})
})