The app-strings module gives you access to the host application's localized string bundles (.properties files).

The module exports the StringBundle constructor function. To access a string bundle, construct an instance of StringBundle, passing it the bundle's URL:

var StringBundle = require("app-strings").StringBundle;
var bundle = StringBundle("chrome://browser/locale/browser.properties");

To get the value of a string, call the object's get method, passing it the name of the string:

var accessKey = bundle.get("contextMenuSearchText.accesskey");
// "S" in the en-US locale

To get the formatted value of a string that accepts arguments, call the object's get method, passing it the name of the string and an array of arguments with which to format the string:

var searchText = bundle.get("contextMenuSearchText",
                            ["universe", "signs of intelligent life"]);
// 'Search universe for "signs of intelligent life"' in the en-US locale

To get all strings in the bundle, iterate the object, which returns arrays of the form [name, value]:

for (var [name, value] in Iterator(bundle))
  console.log(name + " = " + value);

Iteration

for (var name in bundle) { ... }

Iterate the names of strings in the bundle.

for each (var val in bundle) { ... }

Iterate the values of strings in the bundle.

for (var [name, value] in Iterator(bundle)) { ... }

Iterate the names and values of strings in the bundle.