15 javascript snippets

Using js-mode's indent logic in js2-mode

Steve Yegge's js2-mode is a sweet major mode for working with JavaScript in Emacs, but its auto-indentation logic is notoriously frustrating.

Here's a somewhat hack-y workaround: switch to javascript-mode before calling indent-region and then switch back.

;; use js-mode's indent logic, by pressing C-M-| (C-M-S-\)
(defun rlw/js-indent-region () (interactive) (js-mode) (indent-region (region-beginning) (region-end)) (js2-mode) )
(define-key js2-mode-map (kbd "C-M-|") 'rlw/js-indent-region)

PS: I haven't yet had a chance to sort these out, but there are at least four or five JavaScript modes:

The first two are supposed to address js2-mode's indentation problems (among other enhancements).

Published 7 May 2013
Tagged emacs, elisp and javascript.

 

Launching an SSL (HTTPS) Server in Node.js

JavaScript:

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.createServer(config,app).listen(443);

CoffeeScript:

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?

https.createServer(config,app).listen(443)

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):

JavaScript:

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 {
  next();
 }
});

CoffeeScript:

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

JavaScript:

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.");
});

CoffeeScript:

http       = require 'http'
express    = require 'express'
HTTP_PORT  = 80
HTTPS_PORT = 443

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
    else
      res.redirect "https://#{host}#{req.url}", 301
  else
    next()

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) {
    newdiv.setAttribute("style","display:none;")
  } else if(newdiv.style && newdiv.style.setAttribute) {
    newdiv.style.setAttribute("cssText","display:none;")
  } 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
    newdiv.appendChild(newimg)
  });
  document.body.appendChild(newdiv)
}
Published 13 Mar 2014

 

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:

sql_to_html:(connection,query,bindvars,callback)->
  connection.query query, bindvars, (err,rows,fields)->
    if err?
       callback(err)
    else
      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>'
      callback(null,buffer)
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.

escape_for_regexp=(str)->
  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 []
  else
    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]');
  process.exit();
} );

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

flags

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

patterns

  • \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) {
  main();
}

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
  main:()->
    # ...

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

yields

[ ]

but either of

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

or

coffee example.coffee foo.txt bar.png

yield

[ "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("Read:",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("Read:",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.

 

'.gitignore' boilerplate for CoffeeScript/Node.JS projects.

# node.js / coffeescript
#--------------------------------------------------------------------
docs/*.html
docs/docco
lib-cov
lib/*.js
node_modules
README.html
test/*.js

 

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Copyright © 1999 - 2016 Rodney Waldhoff.