There’s a special syntax to work with promises in a more comfortable fashion, called “async/await”.… There’s another keyword, await, that works only inside async functions, and it’s pretty cool.… Can’t use await in regular functions
If we try to use await in a non-async function, there… As stated earlier, await only works inside an async function.… async/await and promise.then/catch
When we use async/await, we rarely need .then, because
The async keyword handles it, we can simply make async next().… Note the await word.… In an async generator, we should add await, like this:… That’s why async generators work with for await...of.… For us it’ll be a simple async iteration for await..of.
Please note:
Promisification is a great approach, especially when you use async/await (covered… later in the chapter Async/await), but not a total replacement for callbacks.
instance:
Or, we could use let module = await… import(modulePath) if inside an async function.
Or, the same without await… To get the response text, await… The submit() function can be rewritten without async/await like this:… Summary.A typical fetch request consists of two await calls:… Or, without await:
Promise.resolve/reject.Methods Promise.resolve and Promise.reject are rarely needed in modern code, because async… /await syntax (we’ll cover it a bit later) makes them somewhat obsolete.… We cover them here for completeness and for those who can’t use async/await for some reason.
We can also use async/await with the help of a promise-based wrapper, like https://github.com/jakearchibald… We can’t insert an async operation like fetch, setTimeout in the middle of a transaction.… keep the operations together, in one transaction, to split apart IndexedDB transactions and “other” async… /await is much more convenient.… For a promise wrapper and async/await the situation is the same.
The async attribute means that a script is completely independent:
The browser doesn’t block on async… Other scripts don’t wait for async scripts, and async scripts don’t wait for them.… an async script (if an async script finishes loading after the page is complete)
…or after an async… script (if an async script is short or was in HTTP-cache)
In other words, async scripts load in the… Dynamic scripts behave as “async” by default.
Also, in the next chapter we’ll learn async generators, which are used to read streams of asynchronously… generated data (e.g paginated fetches over a network) in for await ... of loops.
don’t block DOMContentLoaded
There are two exceptions from this rule:
Scripts with the async… So if DOMContentLoaded is postponed by long-loading scripts, then autofill also awaits.
from response.body:
The result of await… Please note:
Streams API also describes asynchronous iteration over ReadableStream with for await… Call await reader.read() until it’s done.
We gather response chunks in the array chunks.
deferred.Module scripts are always deferred, same effect as defer attribute (described in the chapter Scripts: async… Async works on inline scripts.For non-module scripts, the async attribute only works on external scripts… Async scripts run immediately when ready, independently of other scripts or the HTML document.… For example, the inline script below has async, so it doesn’t wait for anything.… Async works on inline scripts.
URL – the URL to request, a string, can be URL object.
async – if explicitly set to false, then the request… Synchronous requests.If in the open method the third parameter async is set to false, the request is
But two parallel for-ofs is a rare thing, even in async scenarios.
For the future, just note that “Step” command ignores async actions, such as setTimeout (scheduled function
Microtasks are used “under the cover” of await as well, as it’s another form of promise handling.