jquery.overlay.js

var overlay = {
  el: false,
  class: 'overlay',
  show: function(clickCallback) {
    this.el.show()
    if (clickCallback && typeof clickCallback == "function") {
      this.el.off('click').click(clickCallback)
    }
  },
  hide: function() {
    this.el.hide()
  },
  init: function() {
    if (!this.el || !this.el.length) {
      this.el = $('.'+this.class)
    }
    if (!this.el || !this.el.length) {
      this.el = $('<div>', {
        class: this.class
      })
    }
    $('body').append(this.el)
  },
}
overlay.show = overlay.show.bind(overlay)
overlay.hide = overlay.hide.bind(overlay)
overlay.init = overlay.init.bind(overlay)

jquery.overlay.css

.overlay {
  display: none;
  position: fixed;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  background-color: rgba(0,0,0,0.3);
}