19 dev snippets

Launching an SSL (HTTPS) Server in Node.js


var https      = require("https");
var fs         = require("fs");
var key_file   = "/path/to/file.pem";
var cert_file  = "/path/to/file.crt";
var passphrase = "this is optional";
var config     = {
  key: fs.readFileSync(key_file),
 cert: fs.readFileSync(cert_file)
if(passphrase) {
  config.passphrase = passphrase;



https      = require "https"
fs         = require "fs"
key_file   = "/path/to/file.pem"
cert_file  = "/path/to/file.crt"
passphrase = "this is optional"
config     = {
  key:  fs.readFileSync(key_file)
  cert: fs.readFileSync(cert_file)
config.passphrase = passphrase if passphrase?


Where /path/to/file.pem is the path to a file containing an RSA key, generated (for example) by:

openssl genrsa 1024 > /path/to/file.pem

and /path/to/file.crt is the path to a file containing an SSL certificate, generated (for example) by:

openssl req -new -key /path/to/file.pem -out csr.pem
openssl x509 -req -days 365 -in csr.pem -signkey /path/to/file.pem -out /path/to/file.crt
Published 13 Mar 2014


Redirect www.example.com to example.com in Node.js and Express.js

To redirect all paths on the "www" version of a hostname to the "non-www" (domain only) version using Express.js (or Connect):


app.all('/*', function(req, res, next) {
 if(/^www\./.test(req.headers.host)) {
  res.redirect(req.protocol + '://' + req.headers.host.replace(/^www\./,'') + req.url,301);
 } else {


app.all '/*', (req, res, next)->
  if /^www\./.test req.headers.host
    res.redirect "#{req.protocol}://#{req.headers.host.replace(/^www\./,'')}#{req.url}",301
Published 13 Mar 2014


Redirect http: to https: in Node.js and Express.js

To redirect all HTTP requests to the equivalent HTTPS requests using Express.js you can create a simple Express instance that listens on the HTTP port and performs the redirect.


var http       = require('http');
var express    = require('express');
var HTTP_PORT  = 80;
var HTTPS_PORT = 443;

var http_app = express();
http_app.set('port', HTTP_PORT);

http_app.all('/*', function(req, res, next) {
  if (/^http$/.test(req.protocol)) {
    var host = req.headers.host.replace(/:[0-9]+$/g, ""); // strip the port # if any
    if ((HTTPS_PORT != null) && HTTPS_PORT !== 443) {
      return res.redirect("https://" + host + ":" + HTTPS_PORT + req.url, 301);
    } else {
      return res.redirect("https://" + host + req.url, 301);
  } else {
    return next();

http.createServer(http_app).listen(HTTP_PORT).on('listening', function() {
  return console.log("HTTP to HTTPS redirect app launched.");


http       = require 'http'
express    = require 'express'

http_app = express()
http_app.set 'port', HTTP_PORT

http_app.all '/*', (req, res, next)->
  if /^http$/.test req.protocol
    host = req.headers.host.replace /:[0-9]+$/g, "" # strip the port # if any
    if HTTPS_PORT? and HTTPS_PORT isnt 443
      res.redirect "https://#{host}:#{HTTPS_PORT}#{req.url}", 301
      res.redirect "https://#{host}#{req.url}", 301

http.createServer(http_app).listen(HTTP_PORT).on 'listening',()->
  console.log "HTTP to HTTPS redirect app launched."
Published 13 Mar 2014


Preloading images with JavaScript

If your web app dynamically displays certain images and you don't want to make sure that the images are downloaded before they are first displayed, you can pre-fetch the images using some simple javascript.

For single-page apps, this should be sufficient:

function preload_images(urls) {
  urls.forEach( function(i, url ) {
    (new Image()).src = url;

preload_images( [ 'image1.jpg', 'image2.png', 'image3.tiff' ] );

If you want to add a slight delay (so other web assets can load first) use something like:

setTimeout( function() { preload_images( [ 'image1.jpg', 'image2.png', 'image3.tiff' ] ); }, 500) ;

The single-page-app method above loads each image in the array into memory. However, browsers generally won't cache these images, so if the user navigates to another page without viewing the images, they will be lost.

To make the images cachable, it helps to add the image that is created into the actual DOM tree for the page. Here's one way:

function preload_images(urls) {
  var newdiv = document.createElement("div")
  if(newdiv.setAttribute) {
  } else if(newdiv.style && newdiv.style.setAttribute) {
  } else if(newdiv.style) {
    newdiv.style.cssText = "display:none;";
  } else {
    newdiv.style = "display:none;"
  urls.forEach( function(i, url ) {
    var newimg = new Image();
    newimg.src = url
Published 13 Mar 2014


Fixing "Unexpected string" errors with CoffeeScript 1.7 and Mocha 1.17

Recently I've been running into the following error when testing CoffeeScript files using Mocha:

(exports, require, module, __filename, __dirname) { should  = require 'should'
SyntaxError: Unexpected string

The fix is described here on the mocha site.

coffee-script is no longer supported out of the box. CS and similar transpilers may be used by mapping the file extensions (for use with --watch) and the module name. For example --compilers coffee:coffee-script with CoffeeScript 1.6- or --compilers coffee:coffee-script/register with CoffeeScript 1.7+.

In other words, to fix the problem change the argument:

--compilers coffee:coffee-script

on your Mocha command line to:

--compilers coffee:coffee-script/register
Published 11 Feb 2014
Tagged coffeescript, nodejs and dev.


A General Purpose SQL-to-HTML Routine for CoffeeScript/JavaScript/Node.js

Using node-mysql or similar, the following CoffeeScript routine will generate an HTML table containing the data in a SQL result set, including column headings:

  connection.query query, bindvars, (err,rows,fields)->
    if err?
      buffer = '<table border=1><tr>'
      for field in fields
        buffer += "<th>#{field.name}</th>"
      buffer += '</tr>'
      for row in rows
        buffer += '<tr>'
        for field in fields
          buffer += "<td>#{row[field.name]}</td>"
        buffer += '</tr>'
      buffer += '</table>'
Published 8 Feb 2014


escape a string for use in a regular expression

The following function converts reserved characters into backslash-escaped patterns. This allows a literal string to be used within a regular expression.

  return str.replace(/([.?*+^$[\]\\(){}|-])/g, "\\$1")

For example:

var literal = "Who said that?";
var escaped = escape_for_regexp(literal); // yields "Who said that\?"
var regexp = new RegExp(escaped);
console.log(regexp);                      // yields /Who said that\?/
Published 19 Jun 2013


flatten an array in coffeescript

flatten_array = (a)->
  unless a?
    return null
  else if a.length is 0
    return []
    return ( a.reduce (l,r)->l.concat(r) )
Published 23 Jan 2013


gracefully closing node.js applications via signal handling

To make your node.js application gracefully respond to shutdown signals, use process.on(SIGNAL,HANDLER).

For example, to respond to SIGINT (typically Ctrl-c), you can use:

process.on( "SIGINT", function() {
  console.log('CLOSING [SIGINT]');
} );

Note that without the process.exit(), the program will not be shutdown. (This is you chance to override or "trap" the signal.)

Some common examples (in CoffeeScript):

process.on 'SIGHUP',  ()->console.log('CLOSING [SIGHUP]');  process.exit()
process.on 'SIGINT',  ()->console.log('CLOSING [SIGINT]');  process.exit()
process.on 'SIGQUIT', ()->console.log('CLOSING [SIGQUIT]'); process.exit()
process.on 'SIGABRT', ()->console.log('CLOSING [SIGABRT]'); process.exit()
process.on 'SIGTERM', ()->console.log('CLOSING [SIGTERM]'); process.exit()

PS: On Linux (and similar) you can enter kill -l on the command line to see a list of possible signals, and kill -N PID to send signal N to the process with process ID PID.

Published 8 Jan 2013


Cheat Sheet for JavaScript Regular Expressions


  • /pattern/g - global
  • /pattern/i - case-insensitive
  • /pattern/m - multi-line


  • \s - any whitespace character ([\f\n\r\t\v\u00A0\u2028\u2029])
  • \S - any non-whitespace character ([^\f\n\r\t\v\u00A0\u2028\u2029])
  • [\s\S] - commonly used for "anything including newlines (alternative [^])
  • \S - any non-whitespace character ([^\f\n\r\t\v\u00A0\u2028\u2029])

  • \w - any word character (alpha, numeric or underscore) ([a-zA-Z0-9_])

  • \W - any non-word character ([^a-zA-Z0-9_])
  • \d - any digit ([0-9])
  • \D - any non-digit ([^0-9])
  • \cX- control character X (e.g. \cM matches control-M (^M))
  • \b - word boundary (the position between a word char and whitespace)
  • \B - not a word boundary ([^\b]).
  • \xhh - the character with hex code hh
  • \uhhhh - the character with hex code hhhh
Published 18 Jan 2013


Check require.main to test if a Node.js file is run directly

In Node, when a file is run directly from the command line, require.main is set to its module. Hence require.main === module tells you whether or not your script was invoked directly or required by another file.

A JavaScript "main" idiom:

//#!/usr/bin/env node
// file: example.js

function main() {
  // ...

if(require.main === module) {

The main method will run if example.js is invoked via node example.js or ./example.js but not when required within another script (via require('./example'), for example).

A CoffeeScript "main" idiom (using classes, although it doesn't have to):

#!/usr/bin/env coffee
# file: example.coffee
class Example
    # ...

if require.main is module
  (new Example()).main()

The main method will run if example.coffee is invoked via coffee example.coffee or ./example.coffee but not when required within another script (via require('./example'), for example).

Also see the nodejs.org docs.

Published 3 Mar 2013


In node-optimist, argv._ is an array of the "extra" parameters

In substack's node-optimist, you can use argv._ to fetch any parameters remaining after optimist has done its parsing.

For example (in CoffeeScript):

# file: example.coffee
optimist = require 'optimist'
options = {
  'help' : { description:'Show this message and exit.', boolean:true, alias:'h' }
argv = optimist.usage('Usage: $0 [--help]', options).argv

# Now argv._ contains an array "extra" parameters, if any
console.log argv._

For example

coffee example.coffee --help


[ ]

but either of

coffee example.coffee --help foo.txt bar.png


coffee example.coffee foo.txt bar.png


[ "foo.txt", "bar.png" ]
Published 3 Mar 2013


Ruby-like ARGF for Node.js

tokuhirom's node-argf module offers a Ruby-like ARGF for Node.js.

Install via:

npm install argf

or by adding

  "dependencies" : {
    "argf" : "latest"

to your package.json file.

Use ARGF like this:

ARGF = require('argf');
argf = new ARGF();  // create argf based on current
                    // command line parameters or
                    // input streams.

// register a callback for when all input data has been read
argf.on('finished', function() {
  console.log("Done processing all inputs.");

// process the input(s)
argf.forEach( function(line) {
  console.log("From source:",argv.stream.path);

Like Ruby's ARGF, the module assumes any elements in process.argv represent files to process (and uses the input stream if no files are provided.

You can also pass an array to new ARGF() to provide the list of files, which is handy if you're using something like node-optimist. (Note that in node-optimist you can use argv._ to get the remaining parameters after parsing.) For example:

optimist = require('optimist');
ARGF = require('argf');

options = {
  # ...
argv = optimist.usage('Usage: $0 ...', options).argv;

argf = new ARGF(argv._);

argf.on('finished', function() {
  console.log("Done processing all inputs.");

// process the input(s)
argf.forEach( function(line) {
  console.log("From source:",argv.stream.path);
Published 3 Mar 2013


How to determine if two rectangles overlap

// Assuming that x1,y1 and x2,y2 give the upper left and
// lower right coordinates of the rectangles (respectively).
function rectangles_dont_intersect(Ax1,Ay1,Ax2,Ay2,Bx1,By1,Bx2,By2) {
  return (Ax1 < Bx2) && (Ax2 > Bx1) && (Ay1 < By1) && (Ay2 > By2);

function rectangles_intersect(Ax1,Ay1,Ax2,Ay2,Bx1,By1,Bx2,By2) {
  return !rectangles_dont_intersect(Ax1,Ay1,Ax2,Ay2,Bx1,By1,Bx2,By2);
Published 3 Mar 2013
Tagged javascript and dev.


Sorting a Ruby hash by key or value.

by key


by value

h.sort_by {|k,v| v}

Note both forms return an array of key-value pairs (i.e., an array of arrays).

Tagged ruby and dev.


Using Ruby arrays as stacks and queues.

  • array.push appends an element to the array.
  • array.pop removes (and returns) the last element in the array.
  • Hence array.last (and array[-1]) operates like array.peek would if it existed--it returns (but does not remove) the item on the top of the stack.
  • array.shift removes (and returns) the first element in the array.
  • Hence array.shift "pops" an element in a queue-like way--first in, first out. array.first (and array[1]) allow one to "peek" at this element.
> a = [ 1, 2, 3 ]         # => [1, 2, 3]
> a.push 4                # => [1, 2, 3, 4]
> a.pop                   # => 4
> a                       # => [1, 2, 3]
> a.last                  # => 3
> a                       # => [1, 2, 3]
> a.shift                 # => 1
> a                       # => [2, 3]
> a.first                 # => 2
Tagged ruby and dev.


Reading from input files or STDIN in Ruby using ARGF.

ARGF makes it easy for a Ruby script to read from STDIN, a file specified on the command-line argument or multiple files specified on the command line, all through the same interface.

Recall that ARGV array contains the arguments passed to your Ruby script on the command line.

ARGF assumes that any elements that remain in ARGV represent files. Methods like ARGF.each (accepting a block) and ARGF.readlines (returning an array) operate on the concatenation of all files found in ARGV. If ARGV is empty, then ARGF operates on STDIN instead.

For example, a cat-like program could be implemented in Ruby as:

ARGF.each_line { |line| puts line }

When working with optparse, use the parse! method to strip recognized "flag" parameters from ARGV, leaving only the files you want to operate so that ARGF works just like you want it to. For example:

require 'optparse'

options = { }
opt_parser = OptionParser.new do |opt|
  opt.banner = "Usage: #{$0} [OPTIONS]"
  opt.separator  ""
  opt.separator  "OPTIONS"

  opt.on("-h","--heading HEADING","a heading to display.") do |heading|
    options[:heading] = heading

  opt.on("-v","--verbose","be more chatty") do
    options[:verbose] = true

puts options[:heading] unless options[:heading].nil?
ARGF.each_line { |line| puts line }
Tagged ruby, dev and cli.


Split a Ruby array into two halves.

To split a Ruby array into two equally-sized (+/-1) parts:

left,right = a.each_slice( (a.size/2.0).round ).to_a

For example:

a = [1,2,3,4,5]                         # => [1, 2, 3, 4, 5]
a.each_slice( (a.size/2.0).round ).to_a # => [[1, 2, 3], [4, 5]]
Tagged ruby and dev.


Split a Ruby array into N equally-sized parts.

To split a Ruby array into n equally-sized parts:

a.each_slice( (a.size/n.to_f).round ).to_a

For example:

a = [1,2,3,4,5]; n = 3                     # => 3
a.each_slice( (a.size/n.to_f).round ).to_a # => [[1, 2], [3, 4], [5]]
Tagged ruby and dev.


This page was generated at 4:16 PM on 26 Feb 2018.
Copyright © 1999 - 2018 Rodney Waldhoff.