There’s a special syntax to work with promises in a more comfortable fashion, called “async/await”.… Async functions.Let’s start with the async keyword.… As stated earlier, await only works inside an async function.… Async class methods
To declare an async class method, just prepend it with async:… async/await and promise.then/catch
When we use async/await, we rarely need .then, because
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.
The async keyword handles it, we can simply make async next().… The next() method doesn’t have to be async, it may be a regular method returning a promise, but async… Syntax differences between async and regular iterators:
Iterable
Async Iterable
Method to provide… and regular generators:
Generators
Async generators
Declaration
function*
async function*… We can use async generators to process such data.
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.
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.
Or, we could use let module = await import(modulePath) if inside an async
Promise.resolve/reject.Methods Promise.resolve and Promise.reject are rarely needed in modern code, because async… 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… So we have all the sweet “plain async… For a promise wrapper and async/await the situation is the same.
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
Also, in the next chapter we’ll learn async generators, which are used to read streams of asynchronously
don’t block DOMContentLoaded
There are two exceptions from this rule:
Scripts with the async