Get folder of list item using javascript object model in Sharepoint

Suppose that we need to get folder (SP.Folder) where specific list item (SP.ListItem) is located. The following code shows how to do that:

   1: var ctx = SP.ClientContext.get_current();

   2: var file = item.get_file();

   3: ctx.load(file);

   4: ctx.executeQueryAsync(

   5:     Function.createDelegate(this, function (sender, args) {                                

   6:         var folderUrl = file.get_serverRelativeUrl().substring(0,

   7:             file.get_serverRelativeUrl().lastIndexOf("/"));

   8:         var folder = ctx.get_web().getFolderByServerRelativeUrl(folderUrl);

   9:         ctx.load(folder);

  10:         ctx.executeQueryAsync(

  11:             Function.createDelegate(this, function (sender, args) {

  12:                 ...

  13:             }),

  14:             Function.createDelegate(this, function (sender, args) {

  15:                 console.log(args.get_message());

  16:             }));

  17:     }),

  18:     Function.createDelegate(this, function (sender, args) {

  19:         console.log(args.get_message());

  20:     }));

Here at first we load file (SP.File) (lines 2-3), then get relative url (lines 6-7) and by this relative url get folder (lines 8-9). JSOM documentation says that there is SP.ListItem.folder property available, but it always returned error for some reason. May be it will be fixed in future updates.