Js and drop-down list processing problem solving_javascript skills

Copy code The code is as follows:

var obj=document.getElementByIdx("test");
if(0//obj.options.remove(obj.selectedIndex); //IE available
obj.options[obj.selectedIndex]=null;// Both IE FF can
for(var i=0;iobj.options[i].text=" Subitem" i;
obj.options[i].value=i;
}
if(0obj.options [0].selected=true;
}
}