Show / hide options in optionset value

How can i dynamically show/hide the options from option set  by using javascript. I use the following code for remove option 

Xrm.Page.getControl("new_fieldname").removeOption(802790001)

It was working fine .But i need to show the option dynamically using script. I used addOption . but its was not working

How can i show the optionset options dynamically?

Thanks in Advance