Math & Number Manipulations

Table of contents

Arithmatic

Math JS

factorial 

const bang = n => {
  if ( n < 2 ) return 1;
  let fact = 1, i = 2;
  while (i <= n) {fact*=i; i++};
  return fact;
}

factorial big int 

const bigBang = n => {
  if ( n < 2n ) return 1n;
  let fact = 1n, i = 2n;
  while (i <= n) {fact*=i; i++};
  return fact;
}

product 

arr.reduce((a, b) => a * b, 1);

split num into arr of digits 

const digitize = int => {
  let number = parseInt(int);
  let sum = 10;
  let arr = [];

  while (number > 0) {
      val = number % 10;
      sum += val;
      arr.push(val);
      number = (number - val) / 10;
  }
  console.log(sum);
  return arr.reverse();
}

sum 

arr.reduce((a, b) => a + b, 0);

// slow, iterative sum of 1 + 2 + 3 ... + n of known n O(n)
const sum = (n) => {
    let val = 0;
    while (n > 0) {
        val += n; n--;
    }    
    return val;
}

// faster calculation O(1)
const sum2 = n => n * (n + 1)/2;

randomize 

let randomize = list => console.log(list[Math.floor(list.length * Math.random())]); 

(loop = (i) => {
  setTimeout(() => {
    console.log(i);
    if (i--) loop(i);
  }, 300 + Math.floor(Math.random()*200))
})(22);

Time conversions

Convert hh:mm:ss to seconds and back + number formats

convert HHMMSS to seconds 

const toSec = str => str.split(':').reduce((a, time) => (60 * a) + +time);

convert seconds To HHMMSS 

const toHMS = totalSec => {
  const hours = Math.floor((totalSec % (60 * 60 * 24)) / (60 * 60));
  const minutes = Math.floor((totalSec % (60 * 60)) / (60));
  const seconds = Math.floor((totalSec % (60)) );
  // removes all leading zeros
  const hhmmss = `${ hours > 0 ? hours + ":" : "" }${ hours > 0 && minutes < 10 ? '0' + minutes : minutes }:${ seconds < 10 ? '0' + seconds : seconds }`;
  // keeps all leading zeros
  const _0_HMS = `${ hours < 10 ? '0' + hours : hours }:${ minutes < 10 ? '0' + minutes : minutes }:${ seconds < 10 ? '0' + seconds : seconds }`;
  return _0_HMS;
}

Phone Number format

digits to phone number format and back 

const formatPhone = digts => `(${digts.slice(0,3)}) ${digts.slice(3,6)}-${digts.slice(-4)}`;
const phoneToNumString = phone => phone.match(/\d/g).join("");

Currency conversions

This is based off of this freecodecamp guide: How to Format a Number as Currency in JavaScript

currency.js

// format number to US dollar
let usd = new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency: 'USD',
});

let cad = new Intl.NumberFormat('en-CA', {
    style: 'currency',
    currency: 'CAD',
});

// format number to British pounds
let pounds = Intl.NumberFormat('en-GB', {
    style: 'currency',
    currency: 'GBP',
});

// format number to Indian rupee
let rupee = new Intl.NumberFormat('en-IN', {
    style: 'currency',
    currency: 'INR',
});

// format number to Euro
let euro = Intl.NumberFormat('en-DE', {
    style: 'currency',
    currency: 'EUR',
});

// format number to yuan
let yuan = Intl.NumberFormat('cn-CN', {
    style: 'currency',
    currency: 'CNY',
});

// format number to yen
let yen = Intl.NumberFormat('jp-JA', {
    style: 'currency',
    currency: 'JPY',
});

// format number to won
let won = Intl.NumberFormat('kr-KR', {
    style: 'currency',
    currency: 'KRW',
});

'Dollars: ' + USDollar.format(price)
// Dollars: $143,450.00

`Pounds: ${pounds.format(price)}`;
// Pounds: £143,450.00

'Rupees: ' + rupee.format(price);
// Rupees: ₹1,43,450.00

`Euro: ${euro.format(price)}`;
// Euro: €143,450.00

Binary & Ascii math

binary and ascii math

ascii 

a.charCodeAt(0); // get char code int from str char
String.fromCharCode(...nums); // convert list of nums to string

// convert string to arr of char code nums
const charCodes = (string) => {
  let nums = [];
  for (i in string) nums.push(string.charCodeAt(i)); 
  return nums;
}

// convert hex to string
const hex2str = (hex) => {
  let outputNums = [];
  for (let i = 0; i < hex.length; i+=2) {
    const int = parseInt(hex[i+0] + hex[i+1], 16);
    outputNums.push(int);
  }
  return String.fromCharCode(...outputNums);
}

// convert string to hex
const str2hex = (string) => {
  hex = "";
  for (i in string) hex += string.charCodeAt(i).toString("16").padStart(2, '0');
  return hex;
}

integer to binary and back 

const intBin = int => int.toString(2); // must be called as a function to work otherwise it will error
const binInt = bin => parseInt(bin, 2);

const intHex = int => int.toString(16); // must be called as a function to work otherwise it will error
const hexInt = hex => parseInt(hex, 16);

xor encryption to hex and back 

const xor2hex = (input, key) => {
  let output = "";
  const len = key.length;
  const toXorHex = (a, b) => (a ^ b).toString("16").padStart(2, '0');
  for (i in input) {
    output += toXorHex(input.charCodeAt(i), key.charCodeAt(i % len));
  }; 
  return output;
}

const hex2xor = (input, key) => {
  let outputNums = [];
  const len = key.length;
  for (let i = 0; i < input.length; i+=2) {
    const int = parseInt(input[i+0] + input[i+1], 16);
    outputNums.push(int ^ key.charCodeAt(i/2 % len));
  }
  return String.fromCharCode(...outputNums);
}