jquery draggable:如何限制可拖动区域？

$(function() {
  $("#draggable").draggable({
    containment: "#container"
  });
});

$(function() {
  $("#draggable").draggable({
    containment: "window"
  });
});

$(function() {
  $("#draggable").draggable({
    containment: function(element) {
      // 计算限制区域的位置和大小
      var left = 100;
      var top = 100;
      var width = 500;
      var height = 500;

      // 返回限制区域的位置和大小
      return { left: left, top: top, width: width, height: height };
    }
  });
});