<SELECT multiple> - how to allow only one item selected?

Just don't make it a select multiple, but set a size to it, such as:

  <select name="user" id="userID" size="3">
    <option>John</option>
    <option>Paul</option>
    <option>Ringo</option>
    <option>George</option>
  </select>

Working example: https://jsfiddle.net/q2vo8nge/

If the user should select only one option at once, just remove the "multiple" - make a normal select:

  <select name="mySelect" size="3">
     <option>Foo</option>
     <option>Bar</option>
     <option>Foo Bar</option>
     <option>Bar Foo</option>
  </select>

Fiddle

Why don't you want to remove the multiple attribute? The entire purpose of that attribute is to specify to the browser that multiple values may be selected from the given select element. If only a single value should be selected, remove the attribute and the browser will know to allow only a single selection.

Use the tools you have, that's what they're for.

You want only one option by default, but the user can select multiple options by pressing the CTRL key. This is (already) exactly how the SELECT multiple is meant to behave.

See this: http://www.w3schools.com/tags/tryit.asp?filename=tryhtml_select_multiple

Can you please clarify your question?

I am coming here after searching google and change thing at my-end.

So I just change this sample and it will work with jquery at run-time.

$('select[name*="homepage_select"]').removeAttr('multiple')

http://jsfiddle.net/ajayendra2707/ejkxgy1p/5/