alex-cory

/**
 * by definition, primes cannot be negative
 */
const isPrime = value => {
    for(var i = 2; i < value; i++) {
        if(value % i === 0) {
            return false;
        }
    }
    return value > 1;

alex-cory

const isAllUp = s => s.match(/[^a-z]*/)[0].length === s.length
const isAllLow = s => s.match(/[a-z]*/)[0].length === s.length
const isCapitalized = s => s.substring(1, s.length).match(/[a-z]*/)[0].length === s.length - 1 && /^[A-Z]/.test(s)

console.log('All UP? expect: true got -> ', isAllUp('SOMEWORD'))
console.log('All UP? expect: false got -> ', isAllUp('Someword'))
console.log('All UP? expect: false got -> ', isAllUp('someword'))
console.log('All LOW? expect: true got -> ', isAllLow('someword'))
console.log('All LOW? expect: false got -> ', isAllLow('Someword'))
console.log('All LOW? expect: false got -> ', isAllLow('SOMEWORD'))

alex-cory

var uniq = ar => Array.from(new Set(a))
var uniq = ar => [...new Set(a)]

// Others: https://stackoverflow.com/a/9229821/2782583

alex-cory

// does not include special chars
const isUnique = str => !/([a-z0-9]).*?\1/i.test(str)

// includes special chars
const isUnique = str => !/^.*(.).*\1.*$/i.test(str)

alex-cory

import { observer as observe, inject } from 'mobx'
import { withRouter } from 'react-router'
import React, { Component } from 'react'

// I wonder if this works
const observer = stores => Component => withRouter(inject(...stores)(observe(Component)))

@observer('store')
class MyComponent extends Component {
  // ...

alex-cory

const strip = toRemove => ({
  from: str => {
    const pattern = `(${toRemove.split('').join(')(')})`
    return str.replace(RegExp(pattern, 'ig'), c => '')
  }
})

strip('cool').from('coolio') // io

alex-cory

/**
 *    @example
 *    const list = ['a', 'b', 'c', 'c', 'c']
 *    const numOfCs = count(list, letter => letter === 'c')
 *    console.log(numOfCs) // 3
 */
const count = (ls, cb) => ls.reduce((count, item) => cb(item) ? ++count : count, 0)

alex-cory

const isLeapYear = year => new Date(year,1,29).getDate() === 29

alex-cory

// recursive
const isPalindrome = str => {
  if (str.length === 0 || str.length === 1) return true
  if (str[0] === str[str.length - 1]) return isPalindrome(str.slice(1, str.length - 1))
  return false
}

// efficiently in O(n) time
const isPalindrome2 = str => {
  var half = Math.floor(str.length / 2)

alex-cory

/**
 * Handles special characters too
 */
const capitalize = w => w.toLowerCase().replace(/(?:^|\s)\S/g, l => l.toUpperCase());