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removing tutorials meant only to learn

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xfarrow 2024-08-19 16:44:58 +02:00
parent 7f4747ef4c
commit 3b6aac56ae
6 changed files with 0 additions and 249 deletions
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45
tutorials/0_callbacks.js
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// https://javascript.info/callbacks
function execute_action (param, callback) {
if (param == 'something') {
console.log('Executing action: ' + param);
callback(null, Date.now());
} else {
// We can call callback with one argument even if
// the signature states two parameters
callback(new Error('Invalid parameter'));
}
}
function entryPoint () {
/* ===== Begin Simple callback ===== */
execute_action('something', function (error, time_of_completion) {
if (error) {
console.log('Something happened');
} else {
console.log('Time of completion: ' + new Date(time_of_completion).toDateString());
}
});
console.log('I started here!');
/*
Ciò è utile se ad esempio execute_action fa operazioni lente (ad esempio
scrittura su database, connessioni HTTP ecc..) ma abbiamo bisogno
del suo valore di ritorno per continuare una determinata operazione
(in questo caso la data di completamento dell'esecuzione),
senza però bloccare le altre operazioni che non hanno bisogno di tale
valore, in questo caso console.log("I started here!");
Questo però è solo un esempio in quanto le istruzioni verranno
eseguite in maniera sincrona, ma che ci permette di
comprendere le basi di questo meccanismo.
*/
/* ===== End Simple Callback ===== */
}
entryPoint();
// callbacks usually indicate that the
// execution of their code will continue
// asynchronously.

48
tutorials/1_promises.js
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// https://javascript.info/promise-basics
/*
The function passed to Promise is called "executor". When Promise gets
created, the executor gets executed.
When the Promise ends, it should either call the "resolve" or "reject"
callbacks:
resolve(value) — if the job is finished successfully, with result value.
reject(error) — if an error has occurred, error is the error object.
Remember that Promises are not intrensically asyncronous
*/
const promise = new Promise(function (resolve, reject) {
setTimeout(() => resolve('done'), 500);
});
/*
The first argument of .then is a function that runs when the promise is resolved and receives the result.
The second argument of .then is a function that runs when the promise is rejected and receives the error.
*/
promise.then(
result => console.log('The operation was successful. It returned ' + result),
error => console.log('The operation was not successful: ' + error)
);
/*
Or we can pass only one argument if we're interested only in a positive result
*/
promise.then(
result => console.log('The operation was successful. It returned ' + result)
);
/*
Or we can pass only one argument to the method "catch" if we're interested
in negative results only.
promise.catch internally just calls promise.then(null, f)
*/
promise.catch(
error => console.log(error)
);
/*
finally gets always called
*/
promise.finally(
() => console.log('The execution has terminated. Bye')
);

48
tutorials/2_promise_chaining.js
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// https://javascript.info/promise-chaining
// .then() returns a new Promise when you do "return",
// internally calling resolve().
new Promise(function (resolve, reject) {
setTimeout(() => resolve(1), 1);
}).then(function (result) {
console.log(result);
return result * 2;
}).then(function (result) {
console.log(result);
return result * 2;
}).then(function (result) {
console.log(result);
return result * 2;
});
/*
It will print
1
2
4
*/
/*
It means that "then" is internally implemented roughly as follows:
function then(f){
return new Promise(function(resolve, reject) {
resolve(f());
})
}
*/
// Another example:
fetch('http://www.fsf.org')
// .then below runs when the remote server responds
.then(function (response) {
// response.text() returns a new promise that resolves with the full response text
// when it loads
return response.text();
})
.then(function (text) {
// ...and here's the content of the remote file
console.log(text);
});

64
tutorials/3_async-await.js
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// https://javascript.info/async-await
// A async function always returns a promise. Other values are wrapped in a resolved promise automatically.
// Async e Await sono solo "sintassi zuccherina" per rendere l'utilizzo delle Promise più semplice
async function f1 () {
return 1;
}
f1().then(console.log); // 1
// The keyword await makes JavaScript wait until that promise settles and returns its result.
// It can be used in async functions only
// Let’s emphasize: await literally suspends the function execution until the promise settles,
// and then resumes it with the promise result.
async function f2 () {
const promise = new Promise((resolve, reject) => {
setTimeout(() => resolve('done!'), 1000);
});
const result = await promise; // wait until the promise resolves (*)
console.log(result); // "done!"
}
f2();
// Tutto il codice nella stessa funzione (o nello stesso blocco di codice)
// dopo "await" è da considerarsi nel "then()" di una promessa. Pertanto dopo
// await (ma prima del completamento della Promise),
// il flusso di esecuzione va fuori a quel blocco di codice. Ad esempio considera
// il seguente esempio:
async function exampleAsyncFunction () {
console.log('Before await');
await new Promise(function (resolve, reject) {
setTimeout(() => resolve('done'), 500);
}); // Pauses execution here until the promise resolves.
console.log('After await');
}
console.log('Start');
exampleAsyncFunction();
console.log('End');
// Il risultato sarà:
// Start, Before Await, End, After await
// Viene prima "End" e poi "After Await", perché
// dopo await, il flusso di esecuzione ritorna al
// chiamante
// Domande
//
// Why await only works in async function in javascript?
// https://stackoverflow.com/questions/49640647/why-await-only-works-in-async-function-in-javascript
//
// Why using async-await
// https://stackoverflow.com/questions/42624647/why-use-async-when-i-have-to-use-await
//
// Si faccia presente che non è possibile creare da zero una funzione asincrona (come
// setInterval o fetch)
// https://stackoverflow.com/questions/61857274/how-to-create-custom-asynchronous-function-in-javascript
//
// Altra domanda interessante
// https://stackoverflow.com/questions/42624647/why-use-async-when-i-have-to-use-await

12
tutorials/delay.js
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/*
The built-in function setTimeout uses callbacks. Create a promise-based alternative.
The function delay(ms) should return a promise. That promise should resolve after ms milliseconds, so that we can add .then to it, like this:
*/
function delay (ms) {
return new Promise(resolve => {
setTimeout(resolve, ms);
});
}
delay(1000).then(() => console.log('Hello world!'));

32
tutorials/sincrono_vs_asincrono.txt
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Link utili:
https://stackoverflow.com/questions/748175/asynchronous-vs-synchronous-execution-what-is-the-difference
https://stackoverflow.com/questions/7131991/asynchronous-and-synchronous-terms
La parola "sincrono" in contesto informatico vuol dire "sincronizzato", ovvero
il chiamante deve aspettare la risposta del chiamato, mentre
"async" vuol dire "non sincronizzato".
Ciò vuol dire (non)/sincronizzato con altre porzioni di codice.
La definizione da dizionario invece differisce.
Per Treccani: "Sincrono: Che avviene nello stesso momento",
mentre sappiamo che un'operazione sincrona rispetto ad un'altra
non avviene allo stesso tempo.
In informatica dire "un metodo è (a)sincrono" deve
sempre accompagnate da "rispetto a chi" è (a)sincrono.
Possiamo anche pensarla così: (https://stackoverflow.com/a/32052611/18371893)
In a nutshell, synchronization refers to two or more processes' start and end points, NOT their executions.
In this example, Process A's endpoint is synchronized with Process B's start point:
SYNCHRONOUS
|--------A--------|
|--------B--------|
Asynchronous processes, on the other hand, do not have their start and endpoints synchronized:
ASYNCHRONOUS
|--------A--------|
|--------B--------|
Where Process A overlaps Process B, they're running concurrently or synchronously (dictionary definition), hence the confusion.