Node examples, and minor fixes

chapter03/package.json

@@ -5,11 +5,9 @@
     "main": "index.js",
     "scripts": {
         "build": "flow-remove-types src/ -d out/",
-        "buildWithMaps":
-            "flow-remove-types src/ -d out/ --pretty --sourcemaps",
+        "buildWithMaps": "flow-remove-types src/ -d out/ --pretty --sourcemaps",
         "start": "npm run build && node out/doroundmath.js",
-        "nodemon":
-            "./node_modules/nodemon/bin/nodemon.js --watch src --delay 1 --exec npm start",
+        "nodemon": "nodemon --watch src --delay 1 --exec npm start",
         "addTypes": "flow-typed install",
         "update": "npm install && flow-typed install",
         "flow": "flow",
@@ -20,7 +18,10 @@
     "author": "Federico Kereki",
     "license": "ISC",
     "babel": {
-        "presets": ["env", "flow"]
+        "presets": [
+            "env",
+            "flow"
+        ]
     },
     "eslintConfig": {
         "parserOptions": {
@@ -33,21 +34,37 @@
             "node": true,
             "es6": true
         },
-        "extends": ["eslint:recommended", "plugin:flowtype/recommended"],
-        "plugins": ["babel", "flowtype"],
+        "extends": [
+            "eslint:recommended",
+            "plugin:flowtype/recommended"
+        ],
+        "plugins": [
+            "babel",
+            "flowtype"
+        ],
         "rules": {
             "no-console": "off",
             "no-var": "error",
             "prefer-const": "error"
         }
     },
-    "eslintIgnore": ["**/out/*.js"],
+    "eslintIgnore": [
+        "**/out/*.js"
+    ],
     "flow-coverage-report": {
         "concurrentFiles": 1,
-        "excludeGlob": ["node_modules/**"],
-        "includeGlob": ["src/**/*.js"],
+        "excludeGlob": [
+            "node_modules/**"
+        ],
+        "includeGlob": [
+            "src/**/*.js"
+        ],
         "threshold": 90,
-        "type": ["text", "html", "json"]
+        "type": [
+            "text",
+            "html",
+            "json"
+        ]
     },
     "prettier": {
         "tabWidth": 4,

chapter03/src/miniserver.js

@@ -0,0 +1,13 @@
+/* @flow */
+"use strict";
+
+const http = require("http");
+
+http
+    .createServer((req, res) => {
+        res.writeHead(200, { "Content-Type": "text/plain" });
+        res.end("Server alive!");
+    })
+    .listen(8080, "localhost");
+
+console.log("Mini server ready at http://localhost:8080/");

chapter03/src/promisify.js

@@ -0,0 +1,49 @@
+/* @flow */
+"use strict";
+
+const fs = require("fs");
+const util = require("util");
+
+const FILE_TO_READ = "/home/fkereki/MODERNJS/chapter03/src/promisify.js"; // its own source!
+
+// 1. Original error-first style callback
+
+function showFileLength1(fileName: string): void {
+    fs.readFile(fileName, "utf8", (err, text) => {
+        if (err) {
+            throw err;
+        } else {
+            console.log(`1. Reading, old style: ${text.length} bytes`);
+        }
+    });
+}
+showFileLength1(FILE_TO_READ);
+
+// 2. Alternative style using promises
+
+function showFileLength2(fileName: string): void {
+    const readFile = util.promisify(fs.readFile);
+
+    readFile(fileName, "utf8")
+        .then((text: string) => {
+            console.log(`2. Reading with promises: ${text.length} bytes`);
+        })
+        .catch((err: mixed) => {
+            throw err;
+        });
+}
+showFileLength2(FILE_TO_READ);
+
+// 3. Using async/await, and with an arrow function just for variety
+
+const showFileLength3 = async (fileName: string) => {
+    const readFile = util.promisify(fs.readFile);
+
+    try {
+        const text: string = await readFile(fileName, "utf8");
+        console.log(`3. Reading with async/await: ${text.length} bytes`);
+    } catch (err) {
+        throw err;
+    }
+};
+showFileLength3(FILE_TO_READ);

chapter03/src/roundmath.js

@@ -1,13 +1,17 @@
 /* @flow */
 "use strict";
 
+// These won't be exported:
+
 const roundToCents = (x: number): number => Math.round(x * 100) / 100;
 
 const changeSign = (x: number): number => -x;
 
+// The following will be exported:
+
 const addR = (x: number, y: number): number => roundToCents(x + y);
 
-const subR = (x: number, y: number) => addR(x, changeSign(y));
+const subR = (x: number, y: number): number => addR(x, changeSign(y));
 
 const multR = (x: number, y: number): number => roundToCents(x * y);