Totally agree, it is much more important to be able to reason about mutability.<p>I would disagree that it&#x27;s super-easy to reason about var, despite being lexically scoped. It still causes an enormous amount of confusion when loops and callbacks are used together.<p>The PI example only really works because we all know what PI should look like. If you were using someone else&#x27;s constant value and it accidentally got rebound it would be much harder to know.