This turns out to be almost useless information for most of us, since the real problem is not re-assignment, but mutation of the value (in the case of non-primitives).

`const x = 2` feels great emotionally, but `const x = [2]` has the feeling of safety without any of the guarantee.

This is a classic case (quoted from Crockford regularly) of a utility that it sometimes useful and sometimes harmful (aka not useful), and there's a better option (`let`), so the better option should generally be preferred.

I only use `const` (refactor from `let`) when a piece of code is reasonably complete and I'm pretty sure re-assignment will not ever be appropriate. Guessing at that before writing the code is a premature optimization.

And guessing wrongly and having to refactor back to `let` later is more risky.

Const is perfectly sensible with references to mutable objects too. The latter guarantees that x will always point to the same mutable array. If you pass a reference to the x array to a function which needs to mutate that specific array or observe it for changes, then it may be important that x is never rebound to a different array. Consider the following code:

    const x = [5,6,7];

    Object.observe(x, function(changes) {
      console.log('changes', changes);
    });

    // ...
    // time to clear the array

    // WRONG! The code observing changes to the old x array will not see
    // this change or future changes to this new array. Because we used const, this
    // will trigger an error and immediately show us our mistake.
    x = [];

    // CORRECT. This mutates the array instead of creating a new empty array.
    x.length = 0;

This notion (concern) is meaningless in JS, since when you pass any reference, it's always a reference-copy, so there's no value nor assistance that `const` provides.