Enable Disable

Enable Disable

Hey,
I am a newby in JQuerry. I want to disabled item1 when item 2 is null and nable it when it have a value. I use it
   if ( $( "#P1_NEW" ).length ) {
$("#P1_NEW_3").attr('disabled','disabled');
}else{
    ("#P1_NEW_3").attr('enable','enable');
}

It work when Item2 is null--> item1 go disabled

wehen item2
 has a value--> Item is not Enable. 

Can you help me. Thank