Exercises (#12)

Author: shhavel

Exercises/2-closure.js

@@ -0,0 +1,15 @@
+'use strict';
+
+const coffee = (volume, strength) =>
+  `Coffee volume: ${volume}ml, strength: ${strength}`;
+
+const defineCoffeeType = volume => strength => coffee(volume, strength);
+
+// Use function defineCoffeeType to define new coffee types.
+// Define coffee type espresso which volume should equal 50ml.
+// Define coffee type americano which volume should equal 150ml.
+
+const espresso = null;
+const americano = null;
+
+module.exports = { espresso, americano };

Exercises/2-closure.test

@@ -0,0 +1,16 @@
+[{
+  name: 'espresso',
+  length: [30, 70],
+  cases: [
+    ['medium', 'Coffee volume: 50ml, strength: medium'],
+    ['strong', 'Coffee volume: 50ml, strength: strong'],
+  ]
+},
+{
+  name: 'americano',
+  length: [30, 70],
+  cases: [
+    ['medium', 'Coffee volume: 150ml, strength: medium'],
+    ['strong', 'Coffee volume: 150ml, strength: strong'],
+  ]
+}]

Exercises/3-lambda.js

@@ -0,0 +1,11 @@
+'use strict';
+
+const tagged = (pref, str) => `[${pref}] ${str}`;
+
+// Define function tagDate that prepends current date to the string.
+// E.g. tagDate('My String') === '[2019-11-14] My String'
+// Use function tagged to implement tagDate.
+
+const tagDate = null;
+
+module.exports = { tagDate };

Exercises/3-lambda.test

@@ -0,0 +1,18 @@
+({
+  name: 'tagDate',
+  length: [150, 400],
+  test: tagDate => {
+    {
+      const date = new Date().toISOString().substring(0, 10);
+      const expected = `[${date}] Test`;
+      const y = tagDate('Test');
+      if (y !== expected) {
+        throw new Error(`tagDate('Test') === ${y} expected: ${expected}`);
+      }
+    }
+    {
+      const src = tagDate.toString();
+      if (!src.includes('tagged(')) throw new Error('Use function tagged to implement tagDate');
+    }
+  }
+})

Exercises/4-bind.js

@@ -0,0 +1,25 @@
+'use strict';
+
+/*
+  Generalized mean (Hölder mean)
+  Given n numbers a₁, a₂, ... an
+  Define Hk (for k != 0) as the k-th root of the arithmetic mean
+  of the k-th power of a set of numbers
+         ____________________________
+  Hk = ᵏ√ (a₁ᵏ + a₂ᵏ + ... + anᵏ) / n
+*/
+
+const H = (exp, ...args) => {
+  const sum = args.reduce((s, a) => (s + Math.pow(a, exp)), 0);
+  const avg = sum / args.length;
+  return Math.pow(avg, (1 / exp));
+};
+
+// Use method bind() to create new functions from function H.
+// Create function `average` that returns arithmetic mean (H₁) of the arguments.
+// Create function `rootMeanSquare` that returns quadratic mean (H₂).
+
+const average = null;
+const rootMeanSquare = null;
+
+module.exports = { average, rootMeanSquare };

Exercises/4-bind.test

@@ -0,0 +1,16 @@
+([{
+  name: 'rootMeanSquare',
+  length: [10, 70],
+  cases: [
+    [7, 1, 5],
+    [4, 4, 4, 4],
+  ]
+},
+{
+  name: 'average',
+  length: [10, 70],
+  cases: [
+    [3, 4, 6, 7, 5],
+    [4, 4, 4, 4],
+  ]
+}])

Exercises/5-curry.js

@@ -0,0 +1,16 @@
+'use strict';
+
+// Check 4 digit pin.
+const EXPECTED_PIN = '4967';
+const checkPin = (...code) => code.join('') === EXPECTED_PIN;
+
+// Define function curry that accepts the length of the function
+// (amount of function arguments) and the function.
+
+const curry = (length, fn) => (...args) => null;
+
+// Allows to enter pin code by one character,
+// Usage: press('3')('4')('5')('6')
+const press = curry(4, checkPin);
+
+module.exports = { press };

Exercises/5-curry.test

@@ -0,0 +1,42 @@
+({
+  name: 'press',
+  length: [50, 200],
+  test: press => {
+    {
+      const f1 = press('1');
+      if (typeof f1 !== 'function') {
+        throw new Error(`Expected press('1') to be a function.`);
+      }
+    }
+    {
+      const f2 = press('1')('2');
+      if (typeof f2 !== 'function') {
+        throw new Error(`Expected press('1')('2') to be a function.`);
+      }
+    }
+    {
+      const f3 = press('1')('2')('3');
+      if (typeof f3 !== 'function') {
+        throw new Error(`Expected press('1')('2')('3') to be a function.`);
+      }
+    }
+    {
+      const e4 = press('1')('2')('3')('4');
+      if (typeof e4 !== 'boolean') {
+        throw new Error(`Expected press('1')('2')('3')('4') to be a boolean.`);
+      }
+    }
+    {
+      const res = press('1')('2')('3')('4');
+      if (res) {
+        throw new Error(`Expected false when entered wrong pin code.`);
+      }
+    }
+    {
+      const res = press('4')('9')('6')('7');
+      if (!res) {
+        throw new Error(`Expected true when entered correct pin code.`);
+      }
+    }
+  }
+})

Exercises/6-chaining.js

@@ -0,0 +1,15 @@
+'use strict';
+
+// Check 4 digit pin.
+const EXPECTED_PIN = '4967';
+const checkPin = (...code) => code.join('') === EXPECTED_PIN;
+
+// Impement function press
+// that allows to enter pin code by one character,
+// e.g. press('3').press('4').press('5').press('6')
+//
+// For hint use https://github.com/HowProgrammingWorks/Cheatsheet
+
+const press = null;
+
+module.exports = { press };

Exercises/6-chaining.test

@@ -0,0 +1,18 @@
+({
+  name: 'press',
+  length: [50, 200],
+  test: press => {
+    {
+      const res = press('1').press('2').press('3').press('4');
+      if (res) {
+        throw new Error(`Expected false when entered wrong pin code.`);
+      }
+    }
+    {
+      const res = press('4').press('9').press('6').press('7');
+      if (!res) {
+        throw new Error(`Expected true when entered correct pin code.`);
+      }
+    }
+  }
+})