Native objects in JavaScript are already immutable as in you can not change them, only create new objects. Const will not make your object immutable! Try this:

  const foo = {bar: 1}
  foo.bar = 2;

It will only avoid having the pointer re-pointed to another object. It's better to just try avoiding global variables, and use a naming convention like uppercase and/or underscore for constants and global variables.

Const is probably only meant for constants like the name suggests.

I think something like this is pretty safe from reassigning:

  {
    let foo = 1
    ...
  }
  ...

If you want more control over your properties, you can use the ES5 feature "defineproperty" where you can set writeable: false