[hibbelig]

The tax the OP is talking about is not the iteration itself, it's the book-keeping required by the form of the `for` loop.

One example: if you want to iterate over the elements of an array `a` of size `n`, the header of the `for` loop will look like this:

    for (i=0; i<n; i++) {
        element = a[i];
        ...
    }

The `i=0` part is related to knowledge that the first element of an array has index zero, and the `i<n` part kind of follows from it -- if `n` is the length of the array, and `0` is the first index, then `n-1` is the last index.

Compare this to

    a.forEach(function (element) { ... })

Here, you don't have to know that the first index is 0 and you can't make the mistake of writing `<=` where `<` would have been correct.

So the "tax" that the OP is talking about is the cognitive overhead of having to know all these things about the array representation, and making sure to get these details right.