61 lines
2.2 KiB
JavaScript
61 lines
2.2 KiB
JavaScript
// https://javascript.info/async-await
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// An async function always returns a promise. Other values are wrapped in a resolved promise automatically.
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// Async and await are merely syntactic sugar in order to make Promise usage easier
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async function f1 () {
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return 1
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}
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f1().then(console.log) // 1
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// The keyword await makes JavaScript wait until that promise settles and returns its result.
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// It can be used in async functions only.
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// Let’s emphasize: await literally suspends the function execution until the promise settles,
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// and then resumes it with the promise result.
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async function f2 () {
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const promise = new Promise((resolve, reject) => {
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setTimeout(() => resolve('done!'), 1000)
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})
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const result = await promise // wait until the promise resolves (*)
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console.log(result) // "done!"
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}
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f2()
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// The code in the same function after "await"
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// is to be intended in the "then()" of the primise. This means
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// that after await (but before the completion of the Promise),
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// the flow of execution goes out that code block. For example
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// consider the following example:
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async function exampleAsyncFunction () {
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console.log('Before await')
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await new Promise(function (resolve, reject) {
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setTimeout(() => resolve('done'), 500)
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}) // Pauses execution here until the promise resolves.
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console.log('After await')
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}
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console.log('Start')
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exampleAsyncFunction()
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console.log('End')
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// The result will be:
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// Start, Before Await, End, After await
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// "End" comes before "After Await" because the
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// flow of execution goes to the caller
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// when await is invoked.
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// Questions
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//
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// Why await only works in async function in javascript?
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// https://stackoverflow.com/questions/49640647/why-await-only-works-in-async-function-in-javascript
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//
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// Why using async-await
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// https://stackoverflow.com/questions/42624647/why-use-async-when-i-have-to-use-await
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//
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// Be mindful: it is not possible to create an async function from scratch (such as
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// setInterval o fetch)
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// https://stackoverflow.com/questions/61857274/how-to-create-custom-asynchronous-function-in-javascript
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//
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// Another question that may be interesting
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// https://stackoverflow.com/questions/42624647/why-use-async-when-i-have-to-use-await
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