jquery how to make insertBefore work only once, on first click?

jquery

$(function(){
 $('#4').click(function() {
 $('<input name="if4" type="text" value="other price>"').insertBefore('form textarea');
   });
 });

html

    <form>
< input name="name" type="text" value="Enter your name" /><br />
< input name="contacts" type="text" value="Contact info" /><br />
< select name="services">
< option value="1">1</option>
< option value="2">2</option>
< option value="3">3</option>
< option id="4" value="Other">4</option>
< /select><br />
< textarea name="description">Description</textarea><br />
< /form开发者_如何学Python>

And one more question about it, when i press on option number 4 two time,there appears 2 new fields, is there any way how to fix it, that new field appear only 1 time, after first click ?

$(function(){
 $('#4').one('click', function() {
  $('<input name="if4" type="text" value="other price>"').insertBefore('form textarea');
 });
});