The spec just says that when a block "completes" its execution, however that happens (normal completion, an exception, a break/continue statement, etc.) the dis

The spec just says that when a block "completes" its execution, however that happens (normal completion, an exception, a break/continue statement, etc.) the disposal must run. This is the same for "using" as it is for "try/finally". When a process is forcibly terminated, the behavior is inherently outside the scope of the ECMAScript specification, because at that point the interpreter cannot take any further actions. So what happens depends on what kind of object you're talking about. The example in the article is talking about a "stream" from the web platform streams spec. A stream, in this sense, is a JS object that only exists within a JS interpreter. If the JS interpreter goes away, then it's meaningless to ask whether the lock is locked or unlocked, because the lock no longer exists. If you were talking about some kind of OS-allocated resource (e.g. allocated memory or file descriptors), then there is generally some kind of OS-provided cleanup when a process terminates, no matter how the termination happens, even if the process itself takes no action. But of course the details are platform-specific.