JSFiddle - React, Tailwind, and code Playground

by Ray Toal

HTML

<link rel="stylesheet" href="https://code.jquery.com/qunit/qunit-git.css">
<script src="https://code.jquery.com/qunit/qunit-git.js"></script>
<div id="qunit"></div>
<div id="qunit-fixture"></div>

JavaScript

// A homework problem I assigned to the freshmen.

function countOfNegatives(a) {
  return a.filter(x => x < 0).length;
}

function isPrime(n) {
  let LARGEST = 1000000000000;
  if (isNaN(n) || n < 2 || n > LARGEST || n % 1 !== 0) {
    throw new Error('Cannot test this for primality');
  }
  if (n % 2 === 0 && n !== 2) {
    return false;
  }
  for (var d = 3; d * d < n; d += 2) {
    if (n % d === 0) {
      return false;
    }
  }
  return true;
}

function randomBetween(x, y) {
  return x + Math.random() * (y - x);
}

function acronym(s) {
  return s.toLowerCase().split(/\s+/).map(s => s[0]).join('');
}

function median(a, b, c) {
  return a + b + c - Math.min(a, b, c) - Math.max(a, b, c);
}

function occurrences(s, c) {
  let count = 0;
  for (let ch of s) {
    if (ch === c) {
      count += 1;
    }
  }
  return count;
}

function sumOfEvenSquares(a) {
  const even = (x) => x % 2 === 0;
  const square = (x) => x * x;
  const plus = (x, y) => x + y;
  return a.filter(even).map(square).reduce(plus, 0);
}

function prefix(s1, s2) {
  return s1 === '' || s2 === '' || s1.indexOf(s2) === 0 || s2.indexOf(s1) === 0;
}

function Point(latitude, longitude) {
  if (isNaN(latitude) || Math.abs(latitude) > 90) {
    throw "Illegal latitude: " + latitude;
  }
  if (isNaN(longitude) || Math.abs(longitude) > 180) {
    throw "Illegal longitude: " + longitude;
  }
  this.latitude = latitude;
  this.longitude = longitude;
}

Point.prototype.inArcticCircle = function () {
  return this.latitude >= 66.5628;
};

Point.prototype.inAntarcticCircle = function () {
  return this.latitude <= -66.5628;
};

Point.prototype.inTropics = function () {
  return Math.abs(this.latitude) < 23.4372;
};

Point.prototype.antipode = function () {
  return new Point(-this.latitude,
                   (this.longitude < 0) ? 180 + this.longitude : this.longitude - 180);
};


QUnit.test("My negative counter function works", test => {
  test.equal(countOfNegatives([]), 0);
 ...