demo · v131

file handle lifecycle: try/finally vs using

Open a mock file handle, throw a fake parse error mid-read, and watch what each style does. Left side uses try/finally — easy to forget. Right side uses using — disposal is guaranteed by the language. The simulator counts leaks so you can run it many times.

traditional try/finally (and one without)

    using (deterministic dispose)

      the api

      function makeFile(name) {
  return {
    read() { /* ... */ },
    [Symbol.dispose]() { console.log("closed", name); }
  };
}

function read(name) {
  using f = makeFile(name);  // disposed at scope exit, even if read throws
  return f.read();
}

      see also