public/web-development/presentation.git

			@@ -1565,28 +1565,6 @@
			</pre>
			</section>
			<section>
			Lösung: Callback-Hell oder Pyramide des Todes
			<pre>
			<code class="js" data-trim data-line-numbers>
			setTimeout(function() {
			console.log("zweiter");

			setTimeout(function() {
			console.log("Text A");

			setTimeout(function() {
			console.log("Text B");


			}, 2000);
			}, 2000);
			}, 2000);

			console.log("erster");
			</code>
			</pre>
			</section>
			<section>
			Hilfsmittel: Promises
			<pre>
			<code class="js" data-trim data-line-numbers>
			@@ -1638,7 +1616,514 @@
			</pre>
			</section>
			<section>
			Aufgabe: Implementiere die Funktion "delay", um die Promise-Kette lauffähig zu bekommen
			Aufgabe: Implementiere die Funktion "delay"
			<pre>
			<code class="js" data-trim data-line-numbers>
			const delay = function() {
			// implementieren
			}

			console.log("erster");

			delay(2000)
			.then(function () {
			console.log("zweiter");

			return delay(2000);
			})
			.then(function() {
			console.log("Text A");

			return delay(2000);
			})
			.then(function() {
			console.log("Text B");
			})
			</code>
			</pre>
			</section>
			<section>
			Lösung:
			<pre>
			<code class="js" data-trim data-line-numbers>
			const delay = function(ms) {
			return new Promise(function(resolve, reject) {
			setTimeout(function() {
			resolve();
			}, ms);
			});
			}

			console.log("erster");

			delay(2000)
			.then(function () {
			console.log("zweiter");

			return delay(2000);
			})
			.then(function() {
			console.log("Text A");

			return delay(2000);
			})
			.then(function() {
			console.log("Text B");
			})
			</code>
			</pre>
			</section>
			<section>
			Rückgabewerte mit Promises
			<pre>
			<code class="js" data-trim data-line-numbers>
			const p = new Promise(function(resolve, reject) {
			resolve("ok");
			});

			p.then(function(value) {
			console.log(value);
			});
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			ok
			</code>
			</pre>
			</section>
			<section>
			Fehlerbehandlung mit Promises
			<pre>
			<code class="js" data-trim data-line-numbers>
			const p = new Promise(function(resolve, reject) {
			reject(new Error("Fehler"));
			});

			p
			.then(function() {
			console.log("Ich werde nicht aufgerufen")
			})
			.catch(function(e) {
			console.log(e.message);
			});
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Fehler
			</code>
			</pre>
			</section>
			<section>
			Datei lesen mit NodeJS
			<pre>
			<code class="js" data-trim data-line-numbers>
			const fs = require("fs");

			fs.readFile("./hello.txt", {encoding: "utf8"}, function(error, data) {
			console.log(data);
			});
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Hello World!
			</code>
			</pre>
			</section>
			<section>
			Aufgabe: "Promisifiziere" analog zu "delay" in der letzten Aufgabe den Aufruf von fs.readFile()
			<pre>
			<code class="js" data-trim data-line-numbers>
			const fs = require("fs");

			function readFile() {
			// implementieren
			}

			readFile("./hello.txt").then(function(content) {
			console.log(content);
			});
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Hello World!
			</code>
			</pre>
			</section>
			<section>
			Lösung:
			<pre>
			<code class="js" data-trim data-line-numbers>
			const fs = require("fs");

			function readFile(path) {
			return new Promise(function (resolve, reject) {
			fs.readFile(path, {encoding: "utf8"}, function(error, data) {
			resolve(data);
			});
			});
			}

			readFile("./hello.txt").then(function(content) {
			console.log(content);
			});
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Hello World!
			</code>
			</pre>
			</section>
			<section>
			Aufgabe: Nutze die vorherige Lösung nun für eine Promise-Kette, sodass die Inhalte der zwei Dateien "hello.txt" und "hallo.txt" nacheinander ausgegeben werden:
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Hello World!

			Hallo Welt!

			</code>
			</pre>
			</section>
			<section>
			Lösung:
			<pre>
			<code class="js" data-trim data-line-numbers>
			const fs = require("fs");

			function readFile(path) {
			return new Promise(function (resolve, reject) {
			fs.readFile(path, {encoding: "utf8"}, function(error, data) {
			resolve(data);
			});
			});
			}

			readFile("./hello.txt")
			.then(function(content) {
			console.log(content);

			return readFile("./hallo.txt");
			})
			.then(function(content) {
			console.log(content);
			});
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Hello World!

			Hallo Welt!
			</code>
			</pre>
			</section>
			<section>
			<h3>Async - Await</h3>
			<ul>
			<li>Syntaktischer Zucker für Promises</li>
			<li>Nutzung von <code>await</code> nur im Kontext einer <code>async</code>-Funktion möglich</li>
			</ul>
			<pre>
			<code class="js" data-trim data-line-numbers>
			async function wrapper() {
			const p = new Promise(function(resolve, reject) {
			resolve("Hello from Promise!");
			});

			const result = await p;

			console.log(result);
			}

			wrapper();
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Hello from Promise!
			</code>
			</pre>
			</section>
			<section>
			Aufgabe: Schreibe die Lösung der vorherigen Aufgabe nach Async - Await um
			</section>
			<section>
			Lösung:
			<pre>
			<code class="js" data-trim data-line-numbers>
			const fs = require("fs");

			function readFile(path) {
			return new Promise(function (resolve, reject) {
			fs.readFile(path, {encoding: "utf8"}, function(error, data) {
			resolve(data);
			});
			});
			}

			async function wrapper() {
			const content1 = await readFile("./hello.txt");
			const content2 = await readFile("./hallo.txt");

			console.log(content1);
			console.log(content2);
			}

			wrapper();
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			Hello World!

			Hallo Welt!
			</code>
			</pre>
			</section>
			<section>
			<h3>Destructuring</h3>
			<p>Auflösen von komplexen Strukturen</p>
			<pre>
			<code class="js" data-trim data-line-numbers>
			// Objekt destrukturieren (per Attribut-Namen)
			const { a, b } = { a: 1, b: 2 };

			console.log(a);
			console.log(b);

			// Array destrukturieren (per Position)
			const [ c, d ] = [3, 4];

			console.log(c);
			console.log(d);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			1
			2
			3
			4
			</code>
			</pre>
			</section>
			<section>
			<pre>
			<code class="js" data-trim data-line-numbers>
			// Bei Objekten Elemente umbenennen oder auch auslassen
			const { a: x, b: y } = { a: 1, b: 2, c: 3 };

			console.log(x);
			console.log(y);

			// Bei Arrays Elemente auslassen
			const [ , a, b, , c] = [3, 4, 5, 6, 7, 8];

			console.log(a);
			console.log(b);
			console.log(c);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			1
			2
			4
			5
			7
			</code>
			</pre>
			</section>
			<section>
			<pre>
			<code class="js" data-trim data-line-numbers>
			// Verschachteltes Destructuring
			const {a: [, x, ] } = { a: [0, 1, 2]};

			console.log(x);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			1
			</code>
			</pre>
			</section>
			<section>
			Aufgabe: x soll die 5 enthalten
			<pre>
			<code class="js" data-trim data-line-numbers>
			const o = { a: [0, {b: [0, 5]}, 2]};

			const { /* Destructuring-Ausdruck */ } = o;

			console.log(x);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			5
			</code>
			</pre>
			</section>
			<section>
			Lösung:
			<pre>
			<code class="js" data-trim data-line-numbers>
			const o = { a: [0, { b: [0, 5] }, 2]};

			const { a: [, { b: [, x] }]} = o;

			console.log(x);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			5
			</code>
			</pre>
			</section>
			<section>
			Aufgabe: x soll die 3 enthalten
			<pre>
			<code class="js" data-trim data-line-numbers>
			const o = { a: [0, {b: [0, { c: [{ x: 5 }, { d: 3}] }]}, 2]};

			const { /* Destructuring-Ausdruck */ } = o;

			console.log(x);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			3
			</code>
			</pre>
			</section>
			<section>
			Lösung:
			<pre>
			<code class="js" data-trim data-line-numbers>
			const o = { a: [0, {b: [0, { c: [{ x: 5 }, { d: 3}] }]}, 2]};

			const { a: [, {b: [, { c: [, { d: x}] }] }] } = o;

			console.log(x);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			3
			</code>
			</pre>
			</section>
			<section>
			<p>Destructuring zum parallelen Ausführen von mehreren Promises</p>
			<pre>
			<code class="js" data-trim data-line-numbers="1-10\|11-21">
			const fs = require("fs");

			function readFile(path) {
			return new Promise(function (resolve, reject) {
			fs.readFile(path, {encoding: "utf8"}, function(error, data) {
			resolve(data);
			});
			});
			}

			async function wrapper() {
			const [ content1, content2 ] = await Promise.all([
			readFile("./hello.txt"),
			readFile("./hallo.txt")
			]);

			console.log(content1);
			console.log(content2);
			}

			wrapper();
			</code>
			</pre>
			</section>
			<section>
			<h3>Try-Catch-Finally</h3>
			<pre>
			<code class="js" data-trim data-line-numbers>
			function throwError() {
			try {
			throw new Error("Fehler!");
			return "Hello World!";
			}
			catch (e) {
			return e.message;
			}
			finally {
			console.log("Finally wird immer ausgeführt");
			return "Finally!";
			}
			}

			const result = throwError();
			console.log(result);
			</code>
			</pre>
			<pre class="fragment">
			<code class="bash" data-trim data-line-numbers>
			Finally wird immer ausgeführt
			Finally!
			</code>
			</pre>
			</section>
			<section>
			<p>Anwendungsbeispiel für Try-Catch-Finally</p>
			<pre>
			<code class="js" data-trim data-line-numbers>
			function readFromDatabase() {
			try {
			db.connect();
			return db.read();
			}
			catch (e) {
			console.log(e.stack);
			return "";
			}
			finally {
			if (db.open) {
			db.close();
			}
			}
			}
			</code>
			</pre>
			</section>
			<section>
			<h3>Scope</h3>
			<pre>
			<code class="js" data-trim data-line-numbers>
			function a() {
			const x = 5;

			return function() {
			return x * x;
			};
			}

			const squareX = a();
			const result = squareX();

			console.log(result);
			</code>
			</pre>
			<pre>
			<code class="bash" data-trim data-line-numbers>
			25
			</code>
			</pre>
			</section>
			</section>
			</div>