Append doesn't work

//problem: user when clicking on image goes to a dead end
//create an overlay with the large image-Lightbox
var $overlay = $('<div id="overlay"></div>');
//add overlay
$("body").append($overlay);
//an image
//a caption


//1.capture the click event on a link to an image
$("#imageGallery a").click(function(event){
  event.preventDefault();
 var href= $(this).attr("href");
 console.log(href); 
 $overlay.show();
  //1.1show the overlay
  //1.2 update overlay with the image linked in the link
  //1.3 Get child's alt attribute and set caption

  });
//2. Add overlay
  //2.1 an image
  //2.2 a caption
//3. When overlay is clicked 
  //3.1 Hide the overlay