var_with_default.js

// variable REDIRECT_TO may or may not be defined

// what I'd like to do (but raises ReferenceError):
var redirect_to = REDIRECT_TO || "/default/redirect/path";

// working methods that I don't love

// 1
if (typeof(REDIRECT_TO) != "undefined")
  var redirect_to = REDIRECT_TO;
else
  var redirect_to = "/default/redirect/path";

// 2
try { var redirect_to = REDIRECT_TO; } catch() { var redirect_to = "/default/redirect/path"; }

// SOLUTION - you can avoid the ReferenceError by using window.REDIRECT_TO:

var redirect_to = window.REDIRECT_TO || "/default/redirect/path";