HeroCodders.js

const assert = require('assert');

/**
 * Calculates the circle's area for the given radius
 *
 * @param {number} radius
 * @returns {number} cirle's area
 */
function circleArea(radius) {
  if (typeof radius === 'number') {
    return Math.PI * radius * radius;
  }
  // NOTE: other option is to throw an error but it is unusual for js libraries
  return 0;
}

assert.equal(circleArea(1), Math.PI);
assert.equal(circleArea(3), Math.PI * 9);
assert.equal(circleArea(null), 0);
assert.equal(circleArea(Infinity), Infinity);
assert.equal(circleArea(NaN), NaN);



/**
 * Returns true if string's first letter is upper-cased, false otherwise.
 *
 * @param {string} string to test
 * @returns {boolean}
 */
function isFirstUpper(string) {
  if (typeof string === 'string') {
    return /[A-Z]/.test(string.charAt(0));
  }
  return false;
}

assert.equal(isFirstUpper('Hello'), true);
assert.equal(isFirstUpper(''), false);
assert.equal(isFirstUpper(null), false);
assert.equal(isFirstUpper(1), false);