EnvironmentDetection

それぞれの環境における特徴点を洗い出したものが以下になります。

typeof *	Browser	Worker	Node	NW.js	Electron render	Electron main
window	object	-	-	object	object	-
self	object	object	-	object	object	-
global	-	-	object	object	object	object
GLOBAL	-	-	object	-	object	object
document	object	-	-	object	object	-
WorkerLocation	-	object	-	-	-	-
WebView	-	-	-	-	function	-
__dirname	-	-	-	-	string	string
__filename	-	-	-	-	string	string
setTimeout + ""	native	native	custom	native	native	native

var GLOBAL = (this || 0).self || global;

(function(global) {

var inElectron = "__dirname" in global && "__filename" in global;
var hasGlobal  = !!global.global;

global.IN_ELECTRON =  inElectron;
global.IN_BROWSER  = !inElectron && !hasGlobal && "document" in GLOBAL;
global.IN_WORKER   = !inElectron && !hasGlobal && "WorkerLocation" in GLOBAL;
global.IN_NODE     = !inElectron &&  hasGlobal && !/native/.test(setTimeout);
global.IN_NW       = !inElectron &&  hasGlobal &&  /native/.test(setTimeout);

})(GLOBAL);