Fixes, plus function related code

chapter02/src/default_arguments.js

@@ -0,0 +1,39 @@
+/* @flow */
+
+function root(a: number, n: number = 2): number {
+    return a ** (1 / n);
+}
+
+console.log(root(125, 3)); // 5
+console.log(root(4)); // 2
+console.log(root(9, undefined)); // 3
+
+const nthRoot = (a: number, n: number = 2): number => a ** (1 / n);
+
+console.log(nthRoot(64)); // 8
+
+class Counter {
+    count: number; // required by Flow
+
+    constructor(i: number = 0) {
+        this.count = i;
+    }
+
+    inc(n: number = 1) {
+        this.count += n;
+    }
+}
+
+const cnt = new Counter();
+cnt.inc(3);
+cnt.inc();
+cnt.inc();
+console.log(cnt.count); // 5
+
+function nonsense(a = 2, b = a + 1, c = a * b, d = 9) {
+    console.log(a, b, c, d);
+}
+
+nonsense(1, 2, 3, 4); // 1 2 3 4
+nonsense(); // 2 3 6 9
+nonsense(undefined, 4, undefined, 6); // 2 4 8 6

chapter02/src/functional_code.js

@@ -0,0 +1,28 @@
+/* @flow */
+
+type genericFunction = (...args: Array<mixed>) => mixed;
+type higherOrderFunction = genericFunction => genericFunction;
+
+const once: higherOrderFunction = (fn: genericFunction) => {
+    let done = false;
+    return (...args) => {
+        if (!done) {
+            done = true;
+            fn(...args);
+        }
+    };
+};
+
+const sayHello = () => {
+    console.log("Hello!");
+};
+
+sayHello(); // Hello!
+sayHello(); // Hello!
+sayHello(); // Hello!
+
+const sayHelloOnce = once(sayHello);
+
+sayHelloOnce(); // Hello!
+sayHelloOnce(); // (no output)
+sayHelloOnce(); // (no output)

chapter02/src/get_service_with_async_await.js

@@ -14,7 +14,7 @@ async function getMontevideo() {
     try {
         const montevideoData = await get_weather(MONTEVIDEO_UY);
 
-        console.log("Montevideo, with promises");
+        console.log("Montevideo, with async/await");
         console.log(`Montevideo: ${montevideoData.data.length} bytes`);
     } catch (error) {
         console.log(error.message);

chapter02/src/module_conversions.js

@@ -7,14 +7,14 @@ const KILOMETERS_PER_MILE = 1.60934;
 const GRAMS_PER_POUND = 453.592;
 const GRAMS_PER_OUNCE = 28.3495;
 
-const milesToKm: conversion = m => m / KILOMETERS_PER_MILE;
-const kmToMiles: conversion = k => k * KILOMETERS_PER_MILE;
+const milesToKm: conversion = m => m * KILOMETERS_PER_MILE;
+const kmToMiles: conversion = k => k / KILOMETERS_PER_MILE;
 
-const poundsToKg: conversion = p => p / (GRAMS_PER_POUND / 1000);
-const kgToPounds: conversion = k => k * GRAMS_PER_POUND / 1000;
+const poundsToKg: conversion = p => p * (GRAMS_PER_POUND / 1000);
+const kgToPounds: conversion = k => k / (GRAMS_PER_POUND / 1000);
 
-const gramsToOunces: conversion = g => g / GRAMS_PER_OUNCE;
 const ouncesToGrams: conversion = o => o * GRAMS_PER_OUNCE;
+const gramsToOunces: conversion = g => g / GRAMS_PER_OUNCE;
 
 /*
     It's usually preferred to include all "export"