6 ms·
exit(), execve(), and friends do immediately stop execution—I could understand why you'd think a redirect would as well.
by lights0123 1y ago
exit(), execve(), and friends do immediately stop execution—I could understand why you'd think a redirect would as well.
- JoshTriplett 1y agoExactly. Given that JavaScript runs in the context of a page, redirecting off of the page seems like it should act like a "noreturn" function...but it doesn't. That seems like a very easy mistake to make.
- dvt 1y agoThe redirect is an assignment. In no language has a variable assignment ever stopped execution.
- dminik 1y agoThat doesn't seem that obvious to me. You could have a setter that just calls exit and terminates the whole program.
- dvt 1y agoYeah, this is actually a good point, could have a custom setter theoretically that simply looks like assignment, but does some fancy logic. const location = { set current(where) { if (where == "boom") { throw new Error("Uh oh"); // Control flow breaks here } } }; location.current = "boom" // exits control flow, though it looks like assignment, JS is dumb lol
- JoshTriplett 1y ago$ python3 Python 3.13.7 (main, Aug 20 2025, 22:17:40) [GCC 14.3.0] on linux Type "help", "copyright", "credits" or "license" for more information. >>> class MagicRedirect: ... def __setattr__(self, name, value): ... if name == "href": ... print(f"Redirecting to {value}") ... exit() ... >>> location = MagicRedirect() >>> location.href = "https://example.org/" Redirecting to https://example.org/ $
- dvt 1y agoYou're overloading a setter here. It's cute, I did it in JS as well, but I don't really think it's a counterexample. It would be odd to consider this the norm (per the thought process of the original blog post).
- rowanG077 1y agoThis is not some weird thing. Here is a run of the mill example where python can have properties settting do anything at all. And it's designed like that. import sys class Foo: @property def bar(self): return 10 @bar.setter def bar(self, value): print("bye") sys.exit() foo = Foo() foo.bar = 10 Or in C# if you disqualify dynamic languages: using System; class Foo { public int Bar { get { return 10; } set { Console.WriteLine("bye."); Environment.Exit(0); } } } class Program { static void Main() { Foo obj = new Foo(); obj.Bar = 10; } } This is not some esoteric thing in a lot of programming languages.
- dvt 1y agoYou're also overriding a setter. Maybe I'm going against the grain here, but it's absolutely esoteric. The assignment operator is not supposed to have side-effects, and maybe this is the logician in me, but the implication that we should be aware that weird stuff might be happening when we do `x = 5` is fundamentally bonkers.
- JoshTriplett 1y agoYou started with "In no language has a variable assignment ever stopped execution", and now you're saying "The assignment operator is not supposed to have side-effects". location.href is a counterexample, and there are many counterexamples throughout various tools and languages and libraries. Deciding how you think things should work does not affect how things do work, and it's important to understand the latter. (I do agree it's bad practice, but it happens and people do not always fully control the environments they must work with.) And given that location.href does have a side effect, it's not unreasonable for someone to have assumed that that side effect was immediate rather than asynchronous. That said, if you don't like working with such languages, that's all the more reason to select languages where that doesn't happen, which comes back to the point made in the article.
- lock1 1y agoYou could overload operator=() in C++ with a call to exit(), which fulfills "variable assignment that halts the program".
- dvt 1y agoI was ignoring these kinds of fancy overload cases, but even in JS you can mess with setters to get some unexpected behavior (code below).
- BobbyJo 1y agoidk if I'd consider overloading the assignment operator to call a function, then using it, actually an assignment in truth.
- eru 1y agoWell, when you read the source of the caller, it looks exactly like a normal assignment.
- pjmlp 1y agoAnd for a Rust contrived example, making += terminate execution, use std::ops::AddAssign; use std::process; #[derive(Debug, Copy, Clone, PartialEq)] struct Point { x: i32, y: i32, } impl AddAssign for Point { fn add_assign(&mut self, other: Self) { *self = Self { x: self.x + other.x, y: self.y + other.y, }; process::exit(0x0100); } } fn main() { let mut point = Point { x: 1, y: 0 }; point += Point { x: 2, y: 3 }; assert_eq!(point, Point { x: 3, y: 3 }); }
- ordu 1y agoTry this in C: *(int*)0 = 0; Modern C compilers could require you to complicate this enough to confuse them, because their approach to UB is weird, if they saw an UB they could do anything. But in olden days such an assignment led consistently to SIGSEGV and a program termination.
- DannyBee 1y agoUnless you were on systems that mapped address 0 to a writable but always zero value so they could do load and store speculation without worry. IBM did this for a long time
- deleted 1y ago[deleted]
- mabster 1y agoMy favourite were older embedded systems where 0 was an address you actually do interact with. So for some portion of the code you WANT null pointer access. I can't remember the details but I do remember jumping to null to reset the system being pretty common.
- marshray 1y agoProbably the system interrupt table. Index 0 might reference the handler for the non-maskable interrupt NMI, often the same as a power-on reset. I recall that on DOS, Borland Turbo C would detect writes to address 0 and print a message during normal program exit.
- ghurtado 1y agoRANDOMIZE USR 0
- ncruces 1y agoIn Wasm you can read/write whatever to address zero of linear memory. It's still UB as far as clang is concerned so you C code can do whatever. But it won't “crash” on the spot.
- AdieuToLogic 1y ago> The redirect is an assignment. In no language has a variable assignment ever stopped execution. Many languages support property assignment semantics which are defined in terms of a method invocation. In these languages, the method invoked can stop program execution if the runtime environment allows it to do so. For example, source which is defined thusly: foo.bar = someValue Is evaluated as the equivalent of: foo.setBar (someValue)
- kji 1y agoIn Blink setHref is automatically bound to C++ code [1]. I think it's fair to say that anything goes. [1]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/frame/location.cc;bpv=1;bpt=1;l=145?gsn=setHref&gs=KYTHE%3A%2F%2Fkythe%3A%2F%2Fchromium.googlesource.com%2Fcodesearch%2Fchromium%2Fsrc%2F%2Fmain%3Flang%3Dc%252B%252B%3Fpath%3Dthird_party%2Fblink%2Frenderer%2Fcore%2Fframe%2Flocation.cc%235dpUtEs_gNfN7GTs_HuW1d8L5ztFqGh3JuuAWoNXHCU https://source.chromium.org/chromium/chromium/src/+/main:thi...
- sintax 1y agoUntil they don't. A common issue is not checking if the execve() actually worked and thinking nothing after the execve() will execute, which is an assumption that it not always true.
- jacquesm 1y agoSee, that's what they meant about making assumptions upthread: https://man7.org/linux/man-pages/man3/atexit.3.html https://man7.org/linux/man-pages/man3/atexit.3.html