8 Matching Annotations
- Jan 2022
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blog.atomist.com blog.atomist.com
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My gut told me calling an async function from the setTimeout callback was a bad thing. Since the setTimeout machinery ignores the return value of the function, there is no way it was awaiting on it. This means that there will be an unhandled promise. An unhandled promise could mean problems if the function called in the callback takes a long time to complete or throws an error.
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- Dec 2020
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thecodebarbarian.com thecodebarbarian.com
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Remember that async functions always return promises. This promise rejects if any uncaught error occurs in the function. If your async function body returns a promise that rejects, the returned promise will reject too.
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- Oct 2020
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github.com github.com
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Another example:
const expensiveOperation = async (value) => { // return Promise.resolve(value) // console.log('value:', value) await sleep(1000) console.log('expensiveOperation: value:', value, 'finished') return value } var expensiveOperationDebounce = debounce(expensiveOperation, 100); // for (let num of [1, 2]) { // expensiveOperationDebounce(num).then(value => { // console.log(value) // }) // } (async () => { await sleep(0 ); console.log(await expensiveOperationDebounce(1)) })(); (async () => { await sleep(200 ); console.log(await expensiveOperationDebounce(2)) })(); (async () => { await sleep(1300); console.log(await expensiveOperationDebounce(3)) })(); // setTimeout(async () => { // console.log(await expensiveOperationDebounce(3)) // }, 1300)Outputs: 1, 2, 3
Why, if I change it to:
(async () => { await sleep(0 ); console.log(await expensiveOperationDebounce(1)) })(); (async () => { await sleep(200 ); console.log(await expensiveOperationDebounce(2)) })(); (async () => { await sleep(1100); console.log(await expensiveOperationDebounce(3)) })();Does it only output 2, 3?
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- Sep 2020
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svelte.dev svelte.dev
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www.coreycleary.me www.coreycleary.me
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here I wrapped the function call in an IIFE - that's what that (async () => {....})() is if you've never seen it. This is simply because we need to wrap the await call in a function that uses the async keyword, and we also want to "immediately invoke" the function (IIFE = "Immediately Invoked Function Execution") in order to call it.
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developer.mozilla.org developer.mozilla.org
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Here we store the three Promise objects in variables, which has the effect of setting off their associated processes all running simultaneously. Next, we await their results — because the promises all started processing at essentially the same time, the promises will all fulfill at the same time
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By only adding the necessary handling when the function is declared async, the JavaScript engine can optimize your program for you.
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$: (async() => filtered = await getItems())();
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