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

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.