Entry Points

The following captures a conversation from IRC:

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Owen J: Have you run across the idea +of an "entry point" in a runtime yet? (You've definitely used it, just +possibly not known it had a name.)
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Alex L: I have not!
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Owen J: It's the point where the +execution of the outside system -- the OS, the browser, the Node +runtime, whatever -- stops and the execution of your code starts. Some +platforms only give you one: C on Unix is classic, where there's only +two entry points: main and signal handlers (and a lot of apps only use +main). JS gives you a shit fucking ton of entry points.
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Owen J: In a browser, the pageload +process is an entry point: your code gets run when the browser +encounters a <script> tag. So is every event handler. There's none +of your code running when an event handler starts, only the browser +is running. So is every callback from an external service, like +XmlHttpRequest or EventSource or the File APIs. In Node, the top +level of your main script is an entry point, but so is every callback +from an external service.
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Alex L: Ahahahahahahaha oh my +god. There is no way for me to contain them all. everything the light +touches.
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Owen J: This is important for +reasoning about exception handling! In JS, exception handling only +propagates one direction: towards the entry point of this sequence of +function calls.
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Alex L: Yes. This is what I call a +stack trace.
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Owen J: If an exception escapes from +an entry point, the JS runtime logs it, and then the outside runtime +takes over again. That's one of the ways callbacks from external +services fuck up the idea of a stack trace as a map of control flow.
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Alex L: Huh. Yes. Yes I can see +that. I mean, in my world, control flow is a somewhat handwavey idea +right now. I'm starting to understand why so many people hate JS-land.
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Owen J: Sure. But, for example, a +promise chain is a tool for restructuring control flow. In principle, +error handling should provide some kind of map of that, to allow +programmers -- you -- to diagnose how a program reached a given error +state and maybe one day fix the problem. In THIS future, none of them +do that well, though.
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Alex L: Yes. Truly the darkest +timeline, but this reviews why I am having these concerns.
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