geraldfullam

/* Define new prototype methods on Date object. */
// Returns Date as a String in YYYY-MM-DD format.
Date.prototype.toISODateString = function () {
  return this.toISOString().substr(0,10);
};

// Returns new Date object offset `n` days from current Date object.
Date.prototype.toDateFromDays = function (n) {
  n = parseInt(n) || 0;
  var newDate = new Date(this.getTime());

geraldfullam

Math.isPrime = function (n) {
    if (n === 2) { return true; }
    if (n % 2 === 0) { return false; }
    for(let i = 3, s = Math.sqrt(n); i <= s; i += 2) {
        if (n % i === 0) { return false; }
    }
    return n !== 1;
};

// Based on this StackOverflow answer: https://stackoverflow.com/a/40200710/2502532

geraldfullam

import React from 'react'

export function isComponentWithName (el, name) {
  if (typeof name === 'string') {
    return React.isValidElement(el) && name === getDisplayName(el)
  }
  const validRegEx = name instanceof RegExp ? name : new RegExp(name)
  return React.isValidElement(el) && validRegEx.test(getDisplayName(el))
}

geraldfullam

function getRandomIndex(len) {
  return Math.floor(Math.random() * Math.floor(len));
}

function cycleArray(arr, i) {
  return arr.slice(i).concat(arr.slice(0, i))
}

function cycleArrayByRandomIndex() {
  return cycleArray(arr, getRandomIndex(arr.length))