How to change the number of rows in the textarea using jQuery

jQuery(function($){
  $('#foo').focus(function(){
    $(this).attr('rows',5);
  }).blur(function(){
    $(this).attr('rows',1);
  });
});

Or, using less jQuery, less typing, and getting a hair more performance:

jQuery(function($){
  $('#foo')
    .focus(function(){ this.rows=5 })
    .blur( function(){ this.rows=1 });
});

You can try something like this:

     $(document).ready(function(){

    $('#moo').focus(function(){
        $(this).attr('rows', '4');
    });
});

where moo is your textarea.