Add Concept Exercise for 'randomness': Captain's Log

concepts/randomness/.meta/config.json

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+{
+  "blurb": "Random number generation using Math.random()",
+  "authors": ["SneakyMallard"],
+  "contributors":[]
+}

concepts/randomness/about.md

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+# Introduction
+
+Many programs need (apparently) random values to simulate real-world events.
+
+Common, familiar examples include:
+
+- A coin toss: a random value from ('H', 'T').
+- The roll of a die: a random integer from 1 to 6.
+- Shuffling a deck of cards: a random ordering of a card list.
+- The creation of trees and bushes in a 3-D graphics simulation.
+
+Generating truly random values with a computer is a [surprisingly difficult technical challenge][why-randomness-is-hard], so you may see these results referred to as "pseudorandom".
+
+## Generating random numbers
+
+In Javascript, you can generate psuedorandom numbers using the [`Math.random()`][Math.random] function.
+It will return a psuedorandom floating-point number between 0 (inclusive), and 1 (exclusive).
+
+To get a random number between _min_ (inclusive) and _max_ (exclusive) you can use a function something like this:
+
+```javascript
+function getRandomInRange(min, max) {
+  return min + Math.random() * (max - min);
+}
+getRandomInRange(4, 10);
+// => 5.72
+```
+
+## Generating random integers
+
+To generate a random integer, you can use `Math.floor()` or `Math.ceil()` to turn a randomly generated number into an integer.
+
+```exercism/caution
+
+The `Math.random()` function should NOT be used for security and cryptographic applications!!
+
+Instead, you can use the Web Crypto API, which provides various cryptographic functions.
+```
+
+[why-randomness-is-hard]: https://www.malwarebytes.com/blog/news/2013/09/in-computers-are-random-numbers-really-random
+[Math.random]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random

concepts/randomness/introduction.md

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+# Introduction
+
+Many programs need (apparently) random values to simulate real-world events.
+
+Common, familiar examples include:
+
+- A coin toss: a random value from ('H', 'T').
+- The roll of a die: a random integer from 1 to 6.
+- Shuffling a deck of cards: a random ordering of a card list.
+- The creation of trees and bushes in a 3-D graphics simulation.
+
+Generating truly random values with a computer is a [surprisingly difficult technical challenge][why-randomness-is-hard], so you may see these results referred to as "pseudorandom".
+
+## Generating random numbers
+
+In Javascript, you can generate psuedorandom numbers using the [`Math.random()`][Math.random] function.
+It will return a psuedorandom floating-point number between 0 (inclusive), and 1 (exclusive).
+
+To get a random number between _min_ (inclusive) and _max_ (exclusive) you can use a function something like this:
+
+```javascript
+function getRandomInRange(min, max) {
+  return min + Math.random() * (max - min);
+}
+getRandomInRange(4, 10);
+// => 5.72
+```
+
+## Generating random integers
+
+To generate a random integer, you can use `Math.floor()` or `Math.ceil()` to turn a randomly generated number into an integer.
+
+```exercism/caution
+
+The `Math.random()` function should NOT be used for security and cryptographic applications!!
+
+Instead, you can use the Web Crypto API, which provides various cryptographic functions.
+```
+
+[why-randomness-is-hard]: https://www.malwarebytes.com/blog/news/2013/09/in-computers-are-random-numbers-really-random
+[Math.random]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random

concepts/randomness/links.json

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+[
+  {
+    "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random",
+    "description": "MDN: The Math.random() function"
+  }
+]

config.json

@@ -422,6 +422,18 @@
           "type-conversion"
         ],
         "status": "beta"
+      },
+      {
+        "slug": "captains-log",
+        "name": "Captain's Log",
+        "uuid": "65cf28ab-243c-41cb-a720-f324f2cabe28",
+        "concepts": [
+          "randomness"
+        ],
+        "prerequisites": [
+          "numbers",
+          "arithmetic-operators"
+        ]
       }
     ],
     "practice": [
@@ -2851,6 +2863,11 @@
       "uuid": "4e68e39a-e36c-4d2d-8714-eb6482e31ff5",
       "slug": "while-loops",
       "name": "While Loops"
+    },
+    {
+      "uuid": "ca322d6f-0f7e-4a2d-a058-e98a59cdae93",
+      "slug": "randomness",
+      "name": "Randomness"
     }
   ],
   "key_features": [

exercises/concept/captains-log/.docs/hints.md

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+# Hints
+
+## 1. Generate a random starship registry number
+
+- To generate a random number in the range _min_ (inclusive) to _max_ (exclusive) you can use the snippet `min + Math.random()*(max - min)`.
+- There is a [built in function][floor] for turning a floating point number into an integer.
+
+## 2.Generate a random stardate
+
+- To generate a random number in the range _min_ (inclusive) to _max_ (exclusive) you can use the snippet `min + Math.random()*(max - min)`.
+
+## 3. Generate a random planet
+
+- You can use a randomly generated integer as an array index.
+
+[floor]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/floor

exercises/concept/captains-log/.docs/instructions.md

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+## Instructions
+
+Mary is a big fan of the TV series Star Trek: The Next Generation.
+She often plays pen-and-paper role playing games, where she and her friends pretend to be the crew of the Starship Enterprise.
+Mary's character is Captain Picard, which means she has to keep the captain's log.
+She loves the creative part of the game, but doesn't like to generate random data on the spot.
+
+Help Mary by creating random generators for data commonly appearing in the captain's log.
+
+### 1. Generate a random starship registry number
+
+Enterprise (registry number NCC-1701) is not the only starship flying around!
+When it rendezvous with another starship, Mary needs to log the registry number of that starship.
+
+Registry numbers start with the prefix "NCC-" and then use a number from 1000 to 9999 (both inclusive).
+
+Implement the randomShipRegistryNumber() function that returns a random starship registry number.
+
+```javascript
+randomShipRegistryNumber();
+// => "NCC-1947"
+```
+
+### 2. Generate a random stardate
+
+What's the use of a log if it doesn't include dates?
+
+A stardate is a floating point number.
+The adventures of the Starship Enterprise from the first season of The Next Generation take place between the stardates 41000.0 and 42000.0.
+The "4" stands for the 24th century, the "1" for the first season.
+
+Implement the function randomStardate that returns a floating point number between 41000.0 (inclusive) and 42000.0 (exclusive).
+
+```javascript
+randomStardate();
+// => 41458.15721310934
+```
+
+### 3. Generate a random planet
+
+The Starship Enterprise encounters many planets in its travels.
+Planets in the Star Trek universe are split into categories based on their properties.
+For example, Earth is a class M planet.
+All possible planetary classes are: D, H, J, K, L, M, N, R, T, and Y.
+
+Implement the randomPlanetClassfunction.
+It should return one of the planetary classes at random.
+
+```javascript
+randomPlanetClass();
+// => "K"
+```

exercises/concept/captains-log/.docs/introduction.md

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+# Introduction
+
+Many programs need (apparently) random values to simulate real-world events.
+
+Common, familiar examples include:
+
+- A coin toss: a random value from ('H', 'T').
+- The roll of a die: a random integer from 1 to 6.
+- Shuffling a deck of cards: a random ordering of a card list.
+- The creation of trees and bushes in a 3-D graphics simulation.
+
+Generating truly random values with a computer is a [surprisingly difficult technical challenge][why-randomness-is-hard], so you may see these results referred to as "pseudorandom".
+
+## Generating random numbers
+
+In Javascript, you can generate psuedorandom numbers using the [`Math.random()`][Math.random] function.
+It will return a psuedorandom floating-point number between 0 (inclusive), and 1 (exclusive).
+
+To get a random number between _min_ (inclusive) and _max_ (exclusive) you can use a function something like this:
+
+```javascript
+function getRandomInRange(min, max) {
+  return min + Math.random() * (max - min);
+}
+getRandomInRange(4, 10);
+// => 5.72
+```
+
+## Generating random integers
+
+To generate a random integer, you can use `Math.floor()` or `Math.ceil()` to turn a randomly generated number into an integer.
+
+```exercism/caution
+
+The `Math.random()` function should NOT be used for security and cryptographic applications!!
+
+Instead, you can use the Web Crypto API, which provides various cryptographic functions.
+```
+
+[why-randomness-is-hard]: https://www.malwarebytes.com/blog/news/2013/09/in-computers-are-random-numbers-really-random
+[Math.random]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random

exercises/concept/captains-log/.gitignore

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+/node_modules
+/bin/configlet
+/bin/configlet.exe
+/package-lock.json
+/yarn.lock

exercises/concept/captains-log/.meta/config.json

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+{
+  "authors": [
+    "SneakyMallard"
+  ],
+  "files": {
+    "solution": [
+      "captains-log.js"
+    ],
+    "test": [
+      "captains-log.spec.js"
+    ],
+    "exemplar": [
+      ".meta/exemplar.js"
+    ]
+  },
+  "blurb": "Learn about randomness and the Math.random() function while helping Mary generate stardates and starship registry numbers for her Star Trek roleplay."
+}

exercises/concept/captains-log/.meta/design.md

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+# Design
+
+## Goal
+
+The goal of this exercise is to teach the student how to generate psuedorandom numbers in JavaScript.
+
+## Learning objectives
+
+- Know how to generate a random number with `Math.random()`
+- Know how to generate a random number in a range.
+- Know how to generate a random integer.
+
+## Out of scope
+
+- Details of pseudorandom number generation in general.
+- Different algorithms for pseudorandom number generation.
+
+## Concepts
+
+The Concepts this exercise unlocks are:
+
+- `randomness`: Know of the `Math.random()` function and know how to use it to generate random numbers.
+
+## Prerequisites
+
+- `numbers`: Know how numbers work in JavaScript. Know some number methods.

exercises/concept/captains-log/.meta/exemplar.js

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+/// <reference path="./global.d.ts" />
+// @ts-check
+
+/**
+ * Generates a random starship registry number.
+ *
+ * @returns {string} the generated registry number.
+ */
+export function randomShipRegistryNumber() {
+  return 'NCC-' + Math.floor(1000 + Math.random() * 9000);
+}
+
+/**
+ * Generates a random stardate.
+ *
+ * @returns {number} a stardate between 41000 (inclusive) and 42000 (exclusive).
+ */
+export function randomStardate() {
+  return 41000 + Math.random() * 1000;
+}
+
+/**
+ * Generates a random planet class.
+ *
+ * @returns {string} a one-letter planet class.
+ */
+export function randomPlanetClass() {
+  const planetClasses = ['D', 'H', 'J', 'K', 'L', 'M', 'N', 'R', 'T', 'Y'];
+  return planetClasses[Math.floor(Math.random() * 10)];
+}

exercises/concept/captains-log/.npmrc

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+audit=false

exercises/concept/captains-log/LICENSE

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+MIT License
+
+Copyright (c) 2021 Exercism
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

exercises/concept/captains-log/babel.config.js

@@ -0,0 +1,4 @@
+module.exports = {
+  presets: [['@exercism/babel-preset-javascript', { corejs: '3.40' }]],
+  plugins: [],
+};

exercises/concept/captains-log/captains-log.js

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+/// <reference path="./global.d.ts" />
+// @ts-check
+
+/**
+ * Generates a random starship registry number.
+ *
+ * @returns {string} the generated registry number.
+ */
+export function randomShipRegistryNumber() {
+  throw new Error(
+    'Please remove this line and implement the randomShipRegistryNumber() function',
+  );
+}
+
+/**
+ * Generates a random stardate.
+ *
+ * @returns {number} a stardate between 41000 (inclusive) and 42000 (exclusive).
+ */
+export function randomStardate() {
+  throw new Error(
+    'Please remove this line and implement the randomStardate() function',
+  );
+}
+
+/**
+ * Generates a random planet class.
+ *
+ * @returns {string} a one-letter planet class.
+ */
+export function randomPlanetClass() {
+  throw new Error(
+    'Please remove this line and implement the randomStardate() function',
+  );
+}