jschain: parafocus (#1)

This month my goal is to post a small JavaScript project every day of the month. Today’s project is an angular.js app for jumping between paragraphs using the keyboard. Besides navigating between paragraphs it can show paragraphs before or after the current paragraph without leaving the page. This could help if the reader needs to recall a detail from the last paragraph in order to fully understand the current paragraph.

I used these resources to help me get it done:

  • How to listen for key presses with AngularJS – showed me that I wanted was keydown events on the body tag using ng-keydown
  • 5apps – a lot like GitHub pages with Jekyll turned off, except I don’t need to create another branch. Unlike Heroku, free apps don’t go to sleep.

perl -pechop and perl -pechomp

I recently came up with a couple of pipeable perl one-liners. perl -pechop is a shortened form of perl -p -e chop. Here are the parts of it, explained:

  • perl – the perl executable, here for completeness. to learn about the options, type man perlrun into your terminal.
  • -p – perl assumes a loop around the program where it reads each line from the standard input and prints the output. since it’s a single character option that doesn’t take a parameter, it can be grouped with other options.
  • -e – evaluates (runs) the string that’s passed to it. the way perl’s option parser works, when an option takes data, it uses the rest of the command line parameter. so it can be shortened from perl -p -e chop to perl -pechop. This makes it short enough that typing it in often shouldn’t be a problem.
  • chop – the perl subroutine chop takes the current input and chops the last character off it. It’s handy for chopping the newline. For example pwd | perl -pechop will print the current directory to standard output. It can then be piped to the command to save the current directory to the clipboard (pbcopy on mac os x.

Another perl subroutine, chomp, removes the last character of a line but only if it’s the newline character. It’s useful when you don’t know if there’s a newline. The corresponding perl one-liner is perl -pechomp.

the tsj file format

This is a proposal for a new file format.

The TSV file format is very simple. It requires that fields be delimited by tabs, and has a limitation that tabs can’t appear within fields. Newlines are also forbidden inside a field.

The JSON file format is both simple and powerful, but it can be a tiny bit clumsy compared to TSV. Also there is a tradition of putting one JSON object on a line, but that format isn’t JSON, and it doesn’t have a name that’s caught on.

The TSJ file format is a specialization of TSV, where a field is either a JSON expression or a string. Here is how you tell if it’s a string or a JSON expression:

  1. Fields that start with “{“, ‘”‘, “[“, “-“, or the digits (0-9) are treated as JSON expressions. If they don’t parse, it’s invalid TSJ. If you want to store such a value, use a JSON string expression.
  2. Fields that are exactly one of the words “true”, “false”, or “null” are treated as JSON expressions.
  3. All other fields are treated strings.

Strings and JSON expressions are both UTF-8. Fields are not trimmed after they are split by tab characters. A file containing “true\t false\n” will be read as [[true, ” false”]].

Borrowing Backbone’s extend function

If you want to use Backbone.js’s extend function on your own class, all you have to do is this:

var LightModel = function(attributes, options) {
  this.attributes = _.extend({}, attributes);
}

_.extend(LightModel.prototype, Backbone.Events, {
  get: function(key) { return this.attributes[key]; },
  set: function(key_or_values, value) {
    if (typeof key_or_values == 'string') {
      this.attributes[key_or_values] = value;
    } else {
      _.extend(this.attributes, key_or_values);
    }
  }
});

LightModel.extend = Backbone.extend;

Backbone’s extend function is the same between Backbone’s classes. It just uses the prototype it was called with. MyModel1 and MyModel2 in the following example would be equivalent:

var MyModel1 = Backbone.Model.extend({});
var MyModel2 = Backbone.View.extend.call(Backbone.Model, {});

Steve Klabnik on Rails Stacks

Steve Klabnik wrote a great article called Rails has Two Default Stacks. This is the best mental model I’ve found for the major factions within the rails community.

It breaks down if you start considering various deployment options, but I realized that it’s better not to. Deployment stacks can change more rapidly, and have more reasons for needing to change, than development stacks. It is worth just thinking about the development stack, of which testing is a major part. It is the development stack that plays the biggest role in programmer happiness.

If you work on a large project, thinking about just the development side of things will probably make your (Dev)Ops people happy, too.

Upgrading from rails 2.3.5 to rails 2.3.15 on Ubuntu Karmic

Today I upgraded to rails 2.3.5 on a server that had an old version of Ubuntu. This is with an old version of ruby 1.9 that was installed using the Ubuntu packages rather than rvm. Here’s what I had to do:

1. Change the rails version

I changed the version in config/environment.rb to 2.3.15.

RAILS_GEM_VERSION = '2.3.15' unless defined? RAILS_GEM_VERSION

More information here.

2. Turn off yaml and symbol deserialization

Add this to config/environment.rb, just before the last end statement (at the end of the configuration block):

  ActiveSupport::CoreExtensions::Hash::Conversions::XML_PARSING.delete('symbol')
  ActiveSupport::CoreExtensions::Hash::Conversions::XML_PARSING.delete('yaml')

More information here. This is apparently also solved by the rails update above, but since this flaw is so harmful I’m glad to have it fixed in more than one place.

3. Require thread

I got this from a StackOverflow post. I added this to the top of config/boot.rb:

require 'thread'

# Don't change this file!
# Configure your app in config/environment.rb and config/environments/*.rb

It says not to change the file, but in this case I am not changing the file to customize my rails app but to make it work with a newer version. I’m not sure this step was necessary.

3. Upgrade rubygems

I had an old version of rubygems. It was installed with apt-get, so I couldn’t upgrade it with gem update --system. Furthermore, since I was running an old version of Ubuntu, apt-get upgrades weren’t working for me. So instead I uninstalled rubygems and installed it from source.

5. Install the gems

I installed the gems for rails with gem install rails --version 2.3.15 and also installed thin and mysql.

6. Restart the web server

Finally I restarted the web server.

Now, this is just one system configuration and chances are most are different so this may not help you. The uninstalling of rubygems and reinstallation from source took quite a while to figure out so I thought I’d share. If this doesn’t solve your problem, you may leave a comment and if I have time I’ll try to help you figure out what went wrong with yours.

on Bad Ideas

Long ago I realized that it’s often better not to quit a suspected bad idea, but to explore it and learn from it. @substack just gave me more insight into this:

Don’t unpublish your bad ideas. The best argument against a bad idea is to implement it well.

James Halliday (@substack)

The last sentence is key, and applies to more than published bad ideas. In web development, if it is indeed a bad idea, you’re more likely to learn from it, than to cause harm. If it’s a good idea that seems like it’s a bad idea, which turns out to be a good idea, it might be a really good idea.

Running an old rails app

There are a lot of rails 2.3.x apps that have slipped out of maintenance but are still used. When it comes time to add a feature to them, the original developer may be unavailable or may not have the same configuration for running it in development mode. I found myself in that situation and here’s what I did to run it:

  1. Start a new vagrant instance with Ubuntu. This makes things easy to install.
  2. Install rvm and the same ruby version. The project I received had a .rvmrc which specified a version of 1.8.7. The first time I told rvm to install the old version of ruby, I exited after rvm game me a list of packages to install, and installed those packages. Then I told rvm to install ruby again and it worked.
  3. Install the version of rails. It’s in config/environment.rb. Mine was 2.3.5. I ran “gem install rails -v 2.3.5”.
  4. Install dependencies specified in config/environment.rb. On this project it was just prawn, the pdf generator.
  5. Set up the database. This was the usual drill on this project. Nothing different from a new version of rails, except it was mysql instead of mysql2. I installed the Ubuntu database packages (libmysqlclient-devel and mysql-server), set up the database according to config/database.yml, and tried running rake db:migrate and after that failed ran rake db:schema:load.
  6. Go back to an old version of rubygems. I ran “gem update –system 1.5.3”
  7. Go back to an old version of rake. The breaking changes in rake were pretty much the worst thing ever. Switch to the global gemset and uninstall rake, and install rake again with “gem install rake –version=0.8.7”. If you’re having trouble with rake, 0.8.7 is probably the version you’ll want.

After that you’ll hopefully be able to run commands in script/ as well as rake commands.

In my experience it’s enough of a pain to go from 2.3.5 to 2.3.14 that it might be better to just go from 2.3.5 to the latest 3.x version. This will require a lot of changes but it will make the app ready to be worked on by most rails developers again.

PODO: Generalization of POJO

I’m a bit of a software terminology buff. One of the favorite terms that I’ve heard over the years is Plain Old Java Objects, or POJO. It rhymes with pogo, as in pogo stick.

After thinking about a case where a Backbone.js Model might not make the most sense, due to overhead for communicating with servers and publish/subscribe, I came up with the term PODO, or Plain Old Domain Object. I see that a few people have already thought of it.

To me a Plain Old Domain Object is an object which doesn’t also have the responsibility of persisting itself, which Backbone Model objects and ActiveRecord objects are designed to do.

There are reasons why I find myself wanting to use a model object with persistence built in for complex models, but I think if I had the right storage middleware object I’d be comfortable without them. I’d want it to be based on patching rather than full updates. That way I could trigger only the behavior necessary in my PODOs for a given state change.