Example:
// To disable 
$('.myElement').attr('disabled', 'disabled');

// To enable it
$('.myElement').removeAttr('disabled');

// OR you can set attr to "" 
$('.myElement').attr('disabled', '');

// To disable all checkboxs in page
$(":checkbox").attr('disabled', 'disabled');

// Same result different syntax
// To disable
$('.someElement').attr('disabled', true);
// To enable
$('.someElement').attr('disabled', false);

INPUT VALUE
$("#tm111").attr('value', '123');
// or 
$("#tm111").val('123');
 _---------------------------------------------------_

TOGGLE 
// $("#exshippingform").toggle(this.checked);
// $("#exshippingform").slideToggle("slow");
 
 _---------------------------------------------------_
SELECTEDINDEX 
// remove selected option 
$('#ExtraShipping').attr('selectedIndex', '-1');
// set selected option by using selectedIndex
$('#ExtraShipping').selectedIndex = 0;

 _---------------------------------------------------_
// change text content 
//$("#xxx1").text(mytext);

// change html content 
//$("#xxx1").html(mytext);	

 _---------------------------------------------------_
OPTION SELECTED VALUE
showextar = $("#Country option:selected").attr('value')

 _---------------------------------------------------_
checked 
var shipto = $('#sameshipping').attr('checked')