Make Javascript apps environment-aware

When writing client apps, we usually need to connect to the data server. However, this connection is typically different for production and test environments. This post describes a simple way I’ve come up with to solve this little problem.

The client scripts are expecting to read in the environment somehow. A JS file reads it in as some variable say:

   var env;

Okay, the client read in the configuration from a config file that we access using jQuery like so:

  var env;
  $.getJSON( 'config.json', function( json ) {
    env = json;
  });

 And in the configuration file, is a JSON structure for example:

   file: config.json
  {
    data_server : 192.168.1.31:4005
  }

However, that value is different for different deployment environments. So let’s say we save all the different configurations in another file e.g:

  file: config_all.json
  { 
    TEST : { data_server : 192.168.1.31:4005 },
    PROD : { data_server : 192.168.1.31:3005 }
  }

And we’ll need a simple script that can generate the config.json from the config_all.json file. Something like:

  $ configure_env PROD
  or
  $ configure_env TEST

From a project directory standpoint, the config.json file needs to be accessible within the browser while the config_all.json file should be outside. So we end up something like the following structure: 

  project/tools/configure_env
  project/tools/config_all.json
  project/www/js/config.json

Here’s a simple implementation of configure_env in perl:

  #!/usr/bin/env perl

  use strict;
  use warnings;
  use Path::Tiny qw/path/;
  use JSON;

  my $env = $ARGV[0] || 'TEST';   # Defaults to TEST environment
  my $source_file = 'tools/config_all.json';
  my $target_file = 'www/js/config.json';

  my $config_all = decode_json path($source_file)->slurp();
  path($target_file)->spew(encode_json $config_all->{$env});

Now, whenever we need to add an environment-specific value, we just open up config_all.js and put in the value we need and on the client, it becomes accessible.

Perl - Unit Testing

Here's a screenshot how unit testing can be implemented in Perl for the class we defined earlier.

The testing file should be in the ./t subfolder. Execute the tests like so:

Done.

Perl - Inheritance

Here's how to do inheritance in Perl:

This uses the Moose object system which is should probably be used for all large Perl applications. Compare this against the Javascript version.

See this post on how to unit test the classes.