Remove optgroup from selectbox

HTML optgroup element creates a grouping of options within a select  element in web page. You might be working on optgroup in select box. Here is the simple script for the addition and deletion of optgroups. 

 Adding optgroup

    var selectbox = document.getElementById("ProductIssueField");
    var combinationGroup = document.createElement("optgroup");
    combinationGroup.label = GroupName;
    selectbox.appendChild(combinationGroup); 

Removinging optgroup

    var obj = document.getElementById("ALLUSER");
    var ogl=obj.getElementsByTagName('optgroup');
    for (var i=ogl.length-1;i>=0;i--)
      obj.removeChild(ogl[i])