Update:

As of Notepad++ v7.6, use Plugin Admin to install JSTool per this answer

INSTALL

Download it from http://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to plugin directory of Notepad++. Or you can just install "JSTool" from Plugin Manager in Notepad++.

New Notepad++ install and where did PluginManager go? See How to view Plugin Manager in Notepad++

{
  "menu" : {
    "id" : "file",
    "value" : "File",
    "popup" : {
      "menuitem" : [{
      "value" : "New",
          "onclick" : "CreateNewDoc()"
        }, {
          "value" : "Open",
          "onclick" : "OpenDoc()"
        }, {
          "value" : "Close",
          "onclick" : "CloseDoc()"
        }
      ]
    }
  }
}

enter image description here Tip: Select the code you want to reformat, then Plugins | JSTool | JSFormat.