> That brings me to something I really want in JS, actual unmutable values. If you use `const x = new SomeClass()`, you cannot reassign it, but you can change fields. The first time I encountered `const`, I thought it did the opposite. It would be cool if you could declare something (object, array) to be an immutable value.

That sounds like a fundamental mis-understanding. Variables do not hold objects, they hold references to objects.

    const foo = {};
    let bar = foo;

foo and bar hold references to the same object. They do not hold the object themselves. foo's reference can not be changed. It's const. bar's reference can. But the object is independent of both variables.

If you want the object itself to be unmodifiable there's Object.freeze.

    const foo ...

makes foo const. If you wanted a shortcut for making the object constant (vs Object.freeze) it would be something like

    let foo = new const SomeObject()

This doesn't exist but it makes more sense than believing that `const foo` some how makes the object constant. It only makes foo constant (the reference).