using loop controls from within block lambdas

loop-controls.js

Mailbox.prototype.extractContents = function(contacts) {
    let messages = this.messages;

  loop:
    for (let i = 0, n = messages.length; i < n; i++) {
        messages[i].headers.forEach { |header|
            if (header.isSpam())
                continue loop; // the label is not strictly necessary here
            let addresses = header.extractAddresses();
            addresses.forEach { |addr|
                contacts.add(addr.name, addr.email);
            };
        };
    }
};

I think that you have to be a little more specifc about what GOTO behavior truly is. When you have a linear or linear-ish block { a; b; c; d; e} You should be rightfully alarmed if somebody decides to write code to start from c and go onwards. However when you have a structure designed like a machine gun to do the same operations over an arbitrary "Cartridge" you have to be able to allow for bad cartridges to be ejected or skipped over, and potentially, for a particular condition to stop further execution. There is a subtle but important difference between routing out execution in borderline conditions and jumping over important steps in a single iteration, which is explicitly what a true GOTO does. If you argue that aborting execution within a loop amounts to a GOTO, you're not really appreciating the power of the GOTO, and how it can be handily abused.

I commented more verbosely on Isaac's gist, but in short: what about disallowing mixing of block lambda return and normal return in a single function?

I just want to point out that this is what I mean about goto and FUD. Not that labels are true gotos, not that any form of goto is harmful. But that people will want to argue about it. We will be spending a lot of our time correcting people's misconceptions. And in the end, the consensus will be, "look just don't use labels, you don't need them if you know how to write good javascript". They are not a useful feature of javascript and they should be avoided. We've managed to do it for this long. Let's not falter now.

Yes I do realize that I'm the one that first mentioned goto. Call it a preliminary social experiment that served to fully support my hypothesis.