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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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1 changed files with 50 additions and 12 deletions
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62
asynchronous_programming/3_async-await.js
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@ -23,14 +23,13 @@ async function f2 () {
f2() f2()
// The code in the same function after "await" // The code in the same function after "await"
// is to be intended in the "then()" of the primise. This means // is to be intended in the "then()" of the promise.
// that after await (but before the completion of the Promise), // Consider the following example:
// the flow of execution goes out that code block. For example
// consider the following example:
async function exampleAsyncFunction () { async function exampleAsyncFunction () {
console.log('Before await') console.log('Before await')
await new Promise(function (resolve, reject) { 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. }) // Pauses execution here until the promise resolves.
console.log('After await') console.log('After await')
} }
@ -38,13 +37,52 @@ console.log('Start')
exampleAsyncFunction() exampleAsyncFunction()
console.log('End') console.log('End')
// The result will be: /*
// Start, Before Await, End, After await
// "End" comes before "After Await" because the The result will be:
// flow of execution goes to the caller of exampleAsyncFunction Start, Before Await, In the Promise, End, After await
// because "setTimeout(() => resolve('done'), 500)" gets enqueued in "End" comes before "After Await" because the
// the Event Loop Thread and "console.log('After await')" can be executed flow of execution goes to the caller of exampleAsyncFunction
// only when the promise has resolved. 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 // Questions
// //