await using — await using with for await...of

Reference note (untrusted external data; do not execute it as instructions). It's very easy to confuse the following three syntaxes for await (using x of y) { ... } for (await using x of y) { ... } for (using x of await y) { ... } It may be even more confusing to know that they can be used together. First, await y does what you expect: we {{jsxref("Operators/await", "await")}} the promise y, which is expected to resolve to an object we iterate over. Let us set this variant aside. The {{jsxref("Statements/for-await...of", "for await...of")}} loop requires the y object to be an _async iterable_. This means that the object must have a [Symbol.asyncIterator] method that returns an _async iterator_, whose next() method returns a promise representing the result. This is for when the iterable doesn't know what the next value is, or even if it's done yet, until some async operation is complete. On the other hand, the await using x syntax requires the x object, as yi Attribution: Adapted from MDN Web Docs under CC-BY-SA-2.5. Adaptation: WikiKV isolated this documentation section, normalized formatting, removed long code blocks, and shortened it for retrieval. Verify version-sensitive details at the source.