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Update 3_async-await.js

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xfarrow 2025-01-08 15:14:46 +01:00
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commit 7b10c3ce19
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62
asynchronous_programming/3_async-await.js
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@ -23,14 +23,13 @@ async function f2 () {
f2()
// The code in the same function after "await"
// is to be intended in the "then()" of the primise. This means
// that after await (but before the completion of the Promise),
// the flow of execution goes out that code block. For example
// consider the following example:
// is to be intended in the "then()" of the promise.
// Consider the following example:
async function exampleAsyncFunction () {
console.log('Before await')
await new Promise(function (resolve, reject) {
setTimeout(() => resolve('done'), 500)
console.log("In the Promise")
setTimeout(() => resolve(), 500)
}) // Pauses execution here until the promise resolves.
console.log('After await')
}
@ -38,13 +37,52 @@ console.log('Start')
exampleAsyncFunction()
console.log('End')
// The result will be:
// Start, Before Await, End, After await
// "End" comes before "After Await" because the
// flow of execution goes to the caller of exampleAsyncFunction
// because "setTimeout(() => resolve('done'), 500)" gets enqueued in
// the Event Loop Thread and "console.log('After await')" can be executed
// only when the promise has resolved.
/*
The result will be:
Start, Before Await, In the Promise, End, After await
"End" comes before "After Await" because the
flow of execution goes to the caller of exampleAsyncFunction
after setTimeout() gets enqueued in the Event Loop Thread
but before 500ms have elapsed.
+---------------+
| Main |
+---------------+
|
|
v
+----------------------+
|exampleAsyncFunction |
+----------------------+
|
|
v
+---------------+
| Promise |
+---------------+
|
|
v
+----------------------------------------+
|Enqueue resolve() and exit immediately | +--------------------------------+
+----------------------------------------+ -------------------------------> |Wait 500ms in the libuv library |
| +--------------------------------+
| Nothing left to do in the AWAIT, return to caller |
v |
+---------------+ |
| Main | |
+---------------+ |
| |
| |
v |
+-------------------+ |
| Then() of Promise | <-----------------------------------------------------------
+-------------------+
*/
// Questions
//