nearest foregoer node jquery

in javascript experience, i found unequivocally common assign "searching nearest foregoer an component condition (tag name, class,...)".
can parents() slight jquery job? method returned elements parents() predictable? top-to-bottom bottom-to-top?
for impulse i concentration function:

function ancestor(elem, selector) {
  var $elem = $( elem ).parent();
  while( $elem.size() > 0 ) {
    if( $elem.is( selector ) ) 
    relapse $elem;
    else
       $elem = $elem.parent();
  }
  relapse null;
}

can someone tell me there cunning proceed job?