如何分配空值来选择下拉列表？

Question

This works with Google Chrome and IE but not Firefox. For some reaons, Chrome and IE allow blank value to be assigned eventhough it is not part of the dropdown selection.

document.getElementById('dropdownid').value = "";

Note that I have access to jQuery but is not doing what i wanted.

$("#dropdownid").val("");

The above JQuery does not set it to a blank value because blank is not part of the dropdown options. I need to assign "" to the dropdown selectedvalue due to some third party legacy code issues.

Any idea?

Answer 1

将selectedIndex设置为 -1 将清除选择。

document.getElementById('dropdownid').selectedIndex = -1;

Answer 2

Simply change the selectedIndex . EG:

 $(function(){ $dropdown = $("#dropdownid"); alert($dropdown.val()); //alerts "2" $dropdown[0].selectedIndex = -1; //or document.getElementById('dropdownid').selectedIndex = -1; alert($dropdown.val()) //alerts null });

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script> <select id="dropdownid"> <option value="1">1</option> <option value="2" selected="selected">2</option> <option value="3">3</option> </select>

http://jsfiddle.net/kxoytdg8/

Answer 3

Couldn't you add a blank option to the select before setting it?

var jqDropdown = $('#dropdownid');
if (!jqDropdown.find('option[value=""]').length) {
  jqDropdown.prepend($('<option value=""></option>'));
}
jqDropdown.val("");

Answer 4

您是否尝试过取消选择选择中的选项？

$("#dropdownid option").prop("selected", false);

Answer 5

best way is to use $("#dropdownid").html(''); it makes the value null.

Answer 6

2018 jQuery 3.2.1 answer

If you're chaining methods on a jquery selector, $('#selectId').slideUp(600)[0].selectedIndex = -1 appears to work (at least in Chrome) but bothers my 'stick to one syntax/framework' preference.

This also works: $('#selectId').slideUp(600).find('option[selected]').attr('selected', false);

It's a bit longer, but choose the flavor you prefer.

Answer 7

You can try
$(“#elementId”).val('');
eg $(“#CountryDD”).val('');

Answer 8

//We can set empty dropdown add this code in JS script

$("#dropdownList").empty();

Answer 9

$("#dropdownid option[value='']").attr('selected', true)