ecmascript-2017 - w3toppers.com

how to async/await redux-thunk actions?

The Promise approach export default function createUser(params) { const request = axios.post(‘http://www…’, params); return (dispatch) => { function onSuccess(success) { dispatch({ type: CREATE_USER, payload: success }); return success; } function onError(error) { dispatch({ type: ERROR_GENERATED, error }); return error; } request.then(success => onSuccess, error => onError); }; } The async/await approach export default function createUser(params) … Read more

ES2017 – Async vs. Yield

I do not understand why it is necessary to have the async keyword before the function keyword. For the same reason that we have the * symbol before generator functions: They mark the function as extraordinary. They are quite similar in that regard – they add a visual marker that the body of this function … Read more

(ES6) class (ES2017) async / await getter

Update: As others have pointed out, this doesn’t really work. @kuboon has a nice workaround in an answer below here.. You can do this class Foo { get bar() { return (async () => { return await someAsyncOperation(); })(); } } which again is the same as class Foo { get bar() { return new … Read more

Is async await truly non-blocking in the browser?

await p schedules execution of the rest of your function when promise p resolves. That’s all. async lets you use await. That’s (almost) all it does (It also wraps your result in a promise). Together they make non-blocking code read like simpler blocking code. They don’t unblock code. For a responsive UI, offload CPU-intensive work … Read more

async/await inside arrow functions (Array#map/filter)

You can’t do this as you imagine, because you can’t use await if it is not directly inside an async function. The sensible thing to do here would be to make the function passed to map asynchronous. This means that map would return an array of promises. We can then use Promise.all to get the … Read more

Does awaiting a non-Promise have any detectable effect?

await is not a no-op. If the awaited thing is not a promise, it is wrapped in a promise, that promise is awaited. Therefore await changes the execution order (but you should not rely on it nevertheless): console.log(1); (async function() { var x = await 5; // remove await to see 1,3,2 console.log(3); })(); console.log(2); … Read more

Use Async/Await with Axios in React.js

Two issues jump out: Your getData never returns anything, so its promise (async functions always return a promise) will be fulfilled with undefined if it doesn’t reject The error message clearly shows you’re trying to directly render the promise getData returns, rather than waiting for it to settle and then rendering the fulfillment value Addressing … Read more

Property ‘entries’ does not exist on type ‘ObjectConstructor’

You’re quite correct that changing target is the wrong approach and changing lib is the correct approach, however you have specified the wrong version of the language. According to MDN, Object.entries was officially added in the ES2017 specification. “lib”: [“es2017”] is therefore what you must specify instead*. If you wish to add only the declarations … Read more

ES8 Immediately invoked async function expression

Is this ‘a thing’? Yes. It comes up every now and then, e.g. here. They’re known as IIAFEs 🙂 If you want to put focus on the arrow, you could also call them IIAAFs. Are there pitfalls here I should be aware of? Whenever you call a promise-returning function and don’t return the result to … Read more

How to reject in async/await syntax?

Your best bet is to throw an Error wrapping the value, which results in a rejected promise with an Error wrapping the value: } catch (error) { throw new Error(400); } You can also just throw the value, but then there’s no stack trace information: } catch (error) { throw 400; } Alternately, return a … Read more