How to create Javascript constants as properties of objects using const keyword?

Question

How come constants cannot be set as properties of objects which are variables themselves?

const a  = 'constant' // all is well
// set constant property of variable object
const window.b = 'constant' // throws Exception
// OR
var App = {};  // want to be able to extend
const App.goldenRatio= 1.6180339887  // throws Exception

And how come constants passed by reference suddenly become variable? EDIT: I know App won't (or rather... SHOULDN'T) be mutable; this is just an observation...

(function() {
    const App;
    // bunch of code
    window.com_namespace = App;
}());
window.com_namespace; // App
window.com_namespace = 'something else';
window.com_namespace; // 'something else'

How can a nicely organized, extensible, object-oriented, singly namespaced library containing constants be made with these limitations?

EDIT: I believe zi42, but I just have to ask why

Answer 1

You cannot do it with constants. The only possible way to do something that behaves like you want, but is not using constants, is to define a non-writable property:

var obj = {};
Object.defineProperty( obj, "MY_FAKE_CONSTANT", {
  value: "MY_FAKE_CONSTANT_VALUE",
  writable: false,
  enumerable: true,
  configurable: true
});

Regarding your question as to why a const passed to a function becomes variable, the answer is because it's passed by value and not by reference. The function is getting a new variable that has the same value as your constant.

edit: thanks to @pst for noting that objects literals in javascript are not actually "passed by reference", but using call-by-sharing:

Although this term has widespread usage in the Python community, identical semantics in other languages such as Java and Visual Basic are often described as call-by-value, where the value is implied to be a reference to the object.