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function harvesine(pta, ptb) {
  
  const [lat1, lon1] = pta.split(',')
  const [lat2, lon2] = ptb.split(',')
  
  // convert to radians
  const rad1 = (lat1 * Math.PI) / 180;
  const rad2 = (lat2 * Math.PI) / 180;
  const dLat = ((lat2 - lat1) * Math.PI) / 180;
  const dLon = ((lon2 - lon1) * Math.PI) / 180;

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const xlsx = require('xlsx');
const path = require('path');

const exportExcel = (data, workSheetColumnNames, workSheetName, filePath) => {
    const workBook = xlsx.utils.book_new();
    const workSheetData = [
        workSheetColumnNames,
        ... data
    ];
    const workSheet = xlsx.utils.aoa_to_sheet(workSheetData);

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Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

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Some notes about conversion to number in javascript

javascript has lots of methods to convert any value to number

• all methods could be divided into 2 groups: string and native methods
  • String methods are parseInt and parseFloat
  • Native mathods are Number and Math methods

all native methods behave the same way, sometimes with additional transform

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NSSM cheatsheat

• Create a new service
• List parameters for a service
• Set a parameter for a service
• Parameter list

Create a new service

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const createLogger = (backgroundColor, color) => {
  const logger = (message, ...args) => {
    if (logger.enabled === false) {
      return;
    }

    console.groupCollapsed(
      `%c${message}`,
      `background-color: ${backgroundColor}; color: ${color}; padding: 2px 4px;`,
      ...args

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//Regular Expressions List

//Short Tutorial 

\	// the escape character - used to find an instance of a metacharacter like a period, brackets, etc.
.	// match any character except newline
x	// match any instance of x
^x	// match any character except x
[x]	// match any instance of x in the bracketed range - [abxyz] will match any instance of a, b, x, y, or z
|	// an OR operator - [x|y] will match an instance of x or y

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If you've written any kind of validation on user input, like onkeypress then you'll know that sometimes you want to throttle the amount of times your function runs. A good example of this is Ajax based username validation - you don't want to hit the server on every key press, because most users will be able to write their name in around 1/10th of a second, so you should throttle the ajax request until the input is dormant for 100ms.

So with a bit of magic JavaScript making use of the ever useful closure JavaScript offers, we can create a simple method to handle this for us:

function debounce(fn, delay) {
  var timer = null;
  return function () {
    var context = this, args = arguments;
    clearTimeout(timer);
 timer = setTimeout(function () {

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#!/usr/bin/php
<?PHP
// Generates a strong password of N length containing at least one lower case letter,
// one uppercase letter, one digit, and one special character. The remaining characters
// in the password are chosen at random from those four sets.
//
// The available characters in each set are user friendly - there are no ambiguous
// characters such as i, l, 1, o, 0, etc. This, coupled with the $add_dashes option,
// makes it much easier for users to manually type or speak their passwords.
//

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Error:

$ adb devices
List of devices attached
52003c2b58b445db	no permissions (user in plugdev group; are your udev rules wrong?); see [http://developer.android.com/tools/device.html]

Fix: 
1> sudo usermod -aG plugdev $LOGNAME (https://developer.android.com/studio/run/device)
2> lsusb
3> sudo vi /etc/udev/rules.d/51-android.rules