function isExist(elem){
	if(typeof elem !== 'undefined' && typeof elem !== null) {
		return true;
	}else{
		return false;	
	}
}
var addCover = function(){		
  removeCover();
  var coverCss = {
		position: 'fixed',
    zIndex: '100',
		top : '0px',
		left: '0px',
		bottom: '0px',
		right: '0px',
		backgroundColor:'#000',
		opacity: 0.6
  }
  var cover = $('<div id="cover" class="mask"/>');		
  $('body').append(cover.css(coverCss));
}
var removeCover = function(){
	if(isExist($('#cover'))) $('#cover').remove();
}

function popup(target){
  addCover();
  target.css('position','fixed')
      .css("top",($(window).height()-target.height())/2)
      .css("left",($(window).width()-target.width())/2)
      .css("z-index","9999")
      .fadeIn();
  $(".close").on('click',function(){
    removeCover();
		target.fadeOut();
		return false;
  });
}
$('a').on('click',function(){
	popup($('.popup'))
})