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Commit 3fd4cc9

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‎README.md‎

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@@ -230,13 +230,13 @@ as well as based off of the following YouTube videos:
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Check out https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/2-jQuery-ajax-callback
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3. `fetch()-API`, through `Promise`
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3. `Promise`-based, `fetch()-API`
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Check out https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/3-fetch-promise
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Check out https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/3-promise-fetch
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4.`fetch()-API`, through `async/await` syntax
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Through `async/await` syntax
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Check out https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/4-fetch-async-await
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Check out https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/4-promise-fetch-async-await
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<br>
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‎node-crash-course/Node.md‎

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Common built-in functions that are asynchronous and accept callback functions:
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* `setTimeout(function, delay)`
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* `setTimeout(func, delay)`
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* `Event` mechanism
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Check out `async/1-callback/mylogger.js`
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Check out `src/async/1-callback/mylogger.js`
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* Asynchronous requests (AJAX) with native `XMLHttpRequest` and `jQuery` `ajax()` method
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=> <u>Chaining a lot of callback functions => "Callback hell (回调地狱)"</u>
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Check out `async/1-callback/fs_demo.js` as follows:
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Check out `src/async/1-callback/fs_demo.js` as follows:
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```javascript
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const fs = require('fs');
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const path = require('path');
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const testFolderName = path.join(__dirname, 'test');
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const filename = path.join(testFolderName, 'hello.txt');
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// In order to enture the correct execution order, we need to chain the
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// functions as callbacks, resulting in a long callback chain, which is referred
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// to as "callback hell".
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// Create folder
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fs.mkdir(testFolderName, null, err => {
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if (err) throw err;
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console.log('Folder created.');
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// Create file
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// (Equivalent to writing to file)
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fs.writeFile(filename, 'Hello, world!', err => {
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if (err) throw err;
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console.log('Data written.');
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// Write (Append) to file
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fs.appendFile(filename, ' I love Node.js!', err => {
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if (err) throw err;
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console.log('Date appended.');
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// Read file
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fs.readFile(filename, 'utf8', (err, data) => {
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if (err) throw err;
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console.log(`Read data: ${data}`);
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// Rename file
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fs.rename(
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filename,
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* **`Promise` (since ES6 / ES2015)**
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* For usage, check out `src/async/2-promise/fetch_promise.js`, which contains the following code snippet, and https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/3-fetch-promise
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* For basic usage, check out `src/async/2-promise/fetch_demo.js`, which contains the following code snippet, and https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/3-promise-fetch
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```javascript
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const fetch = require('node-fetch');
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// GET request
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fetch('https://jsonplaceholder.typicode.com/users')
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.then(response => response.json())
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```javascript
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const fs = require('fs');
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const somePath = 'test.txt';
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function myExistHandler() {
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console.log('File exists');
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}
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function myNotExistHandler(err) {
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console.error(err);
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}
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const myExistHandler = () => console.log('File exists');
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const myNotExistHandler = err => console.error(err);
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// Originally, with callback functions, we would use "fs.exists()" like this:
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function checkExistWithCallback(path, existHandler, notExistHandler) {
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fs.exists(path, exists => {
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if (exists) {
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}
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});
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}
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checkExistWithCallback(somePath, myExistHandler, myNotExistHandler);
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// In order to avoid "callback hell", we want to do the same thing with Promise
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// like this.
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// checkExistsWithPromise(somePath)
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// .then(myExistHandler)
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// .catch(myNotExistHandler);
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// If we want to the above, we must let "checkExistsWithPromise()" return a
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// Promise (in which we do the necessary work).
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function checkExistsWithPromise(path) {
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return new Promise((resolve, reject) => {
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fs.exists(path, exists => {
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});
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});
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}
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checkExistsWithPromise(somePath)
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.then(myExistHandler)
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.catch(myNotExistHandler);
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```
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* For advantage usage of Promises, including <u>sequential execution (chaining) of multiple Promises</u>, or <u>parallel execution</u>, check out `async/2-promise/promise_advanced.js` as follows:
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* For advantage usage of Promises, including <u>sequential execution (chaining) of multiple Promises</u>, or <u>parallel execution</u>, check out `src/async/2-promise/promise_advanced.js` as follows:
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```javascript
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const { cleanRoom, removeGarbage, winIceCream } = require('../common');
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console.log('With asynchronous programming, this line is printed first.');
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// Sequential execution (chaining)
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// ===== Sequential execution (chaining) =====
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cleanRoom()
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.then(msg => {
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console.log(msg);
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191187
console.log('All finished');
192188
})
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.catch(err => console.log(err));
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// Parallel execution
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// ===== Parallel execution =====
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Promise.all([cleanRoom(), removeGarbage(), winIceCream()])
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.then(values => {
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console.log(values);
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***
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这个syntax sugar是我们对于error handling, 不必再使用`.catch()`方法, 而是可以恢复到传统的synchronous programming的`try/catch`.
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这个syntax sugar使我们对于error handling, 不必再使用`.catch()`方法, 而是可以恢复到传统的synchronous programming的`try/catch`.
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* For usage, check out `src/async/3-async-await/fetch_async_await.js`, which contains the following code snippet, and https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/4-fetch-async-await
225+
* For usage, check out `src/async/3-promise-async-await/fetch_async_await_demo.js`, which contains the following code snippet, and https://github.com/Ziang-Lu/JavaScript-Learning-Notes/tree/master/ajax/4-promise-fetch-async-await
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```javascript
232228
/**
233229
* Same thing as "fetch_promise.js", but with "async/await" syntax sugar.
234230
*/
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const fetch = require('node-fetch');
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238234
// fetch()-API returns a Promise
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240236
// GET request
241237
async function fetchUsers() {
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// This "async" function returns a Promise
243-
244239
try {
245240
const response = await fetch('https://jsonplaceholder.typicode.com/users');
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const users = await response.json(); // response.json() also returns a Promise
@@ -257,19 +252,18 @@
257252
}
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console.log();
259254
}
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fetchUsers();
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```
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* For usage of Promises with `async/await` syntax sugar, check out `async/3-async-await/promise_async_await.js` as follows:
259+
* For usage of Promises with `async/await` syntax sugar, check out `src/async/3-promise-async-await/promise_async_await.js` as follows:
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```javascript
267262
const { cleanRoom, removeGarbage, winIceCream } = require('../common');
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// Sequential execution (chaining)
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// ===== Sequential execution (chaining) =====
270265
async function myRoutine() {
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// This "async" function returns a Promise
272-
273267
try {
274268
let msg = await cleanRoom();
275269
console.log(msg);
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282276
console.error(err);
283277
}
284278
}
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myRoutine();
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// 使得程序looks and feels like synchronous, 虽然实际上只是syntax sugar, under the
289283
// hood还是asynchronous
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291-
// Parallel execution
284+
285+
// ===== Parallel execution =====
292286
async function myRoutineParallel() {
293287
// This "async" function returns a Promise
294-
295288
try {
296289
const messages = await Promise.all([
297290
cleanRoom(),
@@ -304,7 +297,7 @@
304297
console.error(err);
305298
}
306299
}
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myRoutineParallel();
309302
```
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@@ -333,7 +326,7 @@ Node installations and versions are managed by NVM (Node Version Manager).
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334327
```bash
335328
$ nvm install node # Install the latest version
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# Verify that Node has been installed:
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$ nvm which current
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# /Users/Ziang_Lu/.nvm/versions/node/v13.5.0/bin/node

‎node-crash-course/src/async/1-callback/mylogger.js‎

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1-
// TODO: Read docs about "uuidv4" module
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const EventEmitter = require('events');
42
const fs = require('fs');
53
const path = require('path');
@@ -14,7 +12,7 @@ class MyLogger extends EventEmitter {
1412
* @param {string} msg message to log
1513
*/
1614
log(msg) {
17-
// Emit a "message" event (to self)
15+
// Emit a "message" event (to itself)
1816
this.emit('message', { id: uuidv4(), message: msg });
1917
// The second parameter here (the object) will be passed to the "message"
2018
// event listener.
@@ -25,7 +23,6 @@ const txtLogger = new MyLogger();
2523
// Since MyLogger extends EventEmitter, we can register a callback function
2624
// on it for "message" event, specifically on this txtLogger object.
2725
txtLogger.on('message', data => {
28-
// "message" event listener
2926
fs.appendFile(
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path.join(__dirname, 'logs.txt'),
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JSON.stringify(data, null, 2)
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1+
../../references/promise_fetch.js

‎node-crash-course/src/async/2-promise/fetch_promise.js‎

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This file was deleted.

‎node-crash-course/src/async/2-promise/promise_advanced.js‎

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@@ -4,7 +4,7 @@ const { cleanRoom, removeGarbage, winIceCream } = require('../common');
44

55
console.log('With asynchronous programming, this line is printed first.');
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// Sequential execution (chaining)
7+
// ===== Sequential execution (chaining) =====
88
cleanRoom()
99
.then(msg => {
1010
console.log(msg);
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2020
})
2121
.catch(err => console.log(err));
2222

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// Parallel execution
23+
// ===== Parallel execution =====
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2525
// Example 1
2626
Promise.all([cleanRoom(), removeGarbage(), winIceCream()])
@@ -33,7 +33,7 @@ Promise.all([cleanRoom(), removeGarbage(), winIceCream()])
3333
// Promise.race([cleanRoom(), removeGarbage(), winIceCream()])
3434
// .then(value => {
3535
// console.log(value);
36-
// console.log('One finished');
36+
// console.log('First one finished');
3737
// })
3838
// .catch(err => console.log(err));
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