Simple examples

Author: tshemsedinov

JavaScript/1-identifiers.js

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+'use strict';
+
+// Arguments instead of mutable variables
+
+const { PI, sqrt } = Math;
+const square = x => x * x;
+
+// Imperative
+
+const truncatedConeVolume = ({ height, r1, r2 }) => {
+  const k = PI / 3;
+  const sr1 = square(r1);
+  const sr2 = square(r2);
+  return k * height * (sr1 + r1 * r2 + sr2);
+};
+
+const truncatedConeArea = ({ height, r1, r2 }) => {
+  const sr1 = square(r1);
+  const sr2 = square(r2);
+  const l = sqrt(square(height) + square(r2 - r1));
+  return PI * (sr1 + sr2 + l * (r1 + r2));
+};
+
+{
+  const cone = { height: 7, r1: 10, r2: 15 };
+  cone.v = truncatedConeVolume(cone);
+  cone.s = truncatedConeArea(cone);
+  console.dir(cone);
+}
+
+// Functional
+
+const volume = (height, r1, r2) => (PI * height / 3) *
+  (square(r1) + r1 * r2 + square(r2));
+
+const area = (height, r1, r2) => PI * (
+  square(r1) + square(r2) +
+  sqrt(square(height) + square(r2 - r1)) * (r1 + r2)
+);
+
+const cone = (height, r1, r2, volume, area) => ({
+  height, r1, r2, volume, area
+});
+
+const calcCone = ({ height, r1, r2 }) => cone(
+  height, r1, r2, volume(height, r1, r2), area(height, r1, r2)
+);
+
+{
+  const cone = calcCone({ height: 7, r1: 10, r2: 15 });
+  console.dir(cone);
+}

JavaScript/2-condition.js

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+'use strict';
+
+// Calls instead of if statement
+
+const person = {
+  name: 'Marcus Aurelius',
+  born: 121,
+  city: 'Roma',
+};
+
+// Imperative
+
+{
+  let output = `${person.born} `;
+  if (person.born < 0) {
+    output += 'BC';
+  } else {
+    output += 'AD';
+  }
+  output = `${person.name} was born in ${output}`;
+  console.dir(output);
+}
+
+// Functional
+
+{
+  const era = year => (year < 0 ? 'BC' : 'AD');
+  const { name, born } = person;
+  const output = `${name} was born in ${born} ${era(born)}`;
+  console.dir(output);
+}

JavaScript/3-iteration.js

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+'use strict';
+
+// Call or recursion instead of for loops
+
+const numbers = [2, 7, -1, -5, 8];
+
+// Imperative
+
+for (let i = 0; i < numbers.length; i++) {
+  const n = numbers[i];
+  console.log(`Item ${i} is ${n}`);
+}
+console.log();
+
+// Loop function
+
+const loop = (min, max, fn) => {
+  for (let i = 0; i < max; i++) fn(i);
+};
+
+loop(0, numbers.length, i => {
+  const n = numbers[i];
+  console.log(`Item ${i} is ${n}`);
+});
+
+console.log();
+
+// Recursion
+
+const iterate = (arr, fn, i = 0) => {
+  if (i === arr.length) return;
+  fn(arr[i], i);
+  iterate(arr, fn, ++i);
+};
+
+iterate(numbers, (n, i) => {
+  console.log(`Item ${i} is ${n}`);
+});
+
+console.log();
+
+// forEach
+
+numbers.forEach((n, i) => {
+  console.log(`Item ${i} is ${n}`);
+});

JavaScript/4-arguments.js

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+'use strict';
+
+// Single argument instead of multiple
+
+// Imperative
+
+const max = (a, b) => {
+  if (a > b) return a;
+  else return b;
+};
+console.log(max(3, 5));
+
+// Functional
+
+const maxc = a => b => (a > b ? a : b);
+console.log(maxc(3)(5));

JavaScript/5-instance.js

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+'use strict';
+
+// Closure context instead of object context
+
+// Imperative
+
+const marcus = {
+  name: 'Marcus Aurelius',
+  born: 121,
+  get era() {
+    return this.born < 0 ? 'BC' : 'AD';
+  },
+  toString() {
+    return `${this.name} was born in ${this.born} ${this.era}`;
+  },
+};
+
+console.log(`${marcus}`);
+
+// Functional
+
+const era = year => (year < 0 ? 'BC' : 'AD');
+const person = (name, born) => () => `${name} was born in ${born} ${era(born)}`;
+
+const marcus2 = person('Marcus Aurelius', 121, 'Roma');
+
+console.log(marcus2());