canihaz - supercharged dependency loading and installation

Canihaz is a module that allows you to lazily install and require NPM modules that might not be required for the core functionality of your library. This includes, but is not limited to:

• Optional dependencies
• Dependencies that are only used for your optional CLI interface
• Dependencies that are sparsely used in the application

My use case for this library is a front-end build system that I have been developing. It's called square and uses a plugin based system to process your front-end code such as CSS, JavaScript and all possible pre-processors. If I wanted to support every CSS pre-processor I would have had to specify: sass, less and stylus in the dependencies, but nobody is ever going to use all of them, so 90% of these modules would have been pointless bloat. And I, personally hate code bloat. It's a disease that spreads exponentially with every module that is released and dependent upon. So to combat this bloat I wanted to have a way to lazy load and (silently) install the modules when they are needed.

Table of Contents

• Installation
• How does it work
• API
  • package.json example
  • Configuration
  • Configured dependencies
  • Un-configured dependencies
  • Multiple dependencies
• Changelog
• License

Installation

This module should be installed using NPM:

npm install canihaz --save

The --save parameter tells NPM that it should add it to your package.json, so less editing for you.

If you do not install it using NPM, make sure that install it in a node_modules folder and do not symlink it.. Unless you don't want to use the automatic dependency resolution.

How does it work

I always tell people that you should understand how a module works before you use it, checkout out the source or at least read the damned documentation.

When you initialize the module after you required it it will go up 2 directories to go out of the node_modules folder and attempt to read out the package.json file of the module that depends on canihaz. It requires the package.json and search for the dependencies, it searches for canihaz key by default but it can be configured. When it found the dependencies, it attaches the names to the returned object and creates a really simple usable interface for it:

var canihaz = require('canihaz')(.. config ..);

canihaz.dep(function requireallthethings(err, dep) {
  .. dep is installed if it's not installed before or just required
});

It automatically knows which version it should install for you as you specified that in the object. Installing a dependency that isn't pre-defined in your package.json you could do something similar:

var canihaz = require('canihaz')();

canihaz(dep, version, function lazyloading(err, dep) {
  .. dep is installed with the specified version
});

But before it tries to install the module it checks it it's perhaps globally installed (with the correct version) or if it's already installed before in the specified location. When all these checks fail, we continue with the installation. In older version of canihaz we called the NPM api programatically but there were a couple of issues with this, like install race conditions and it didn't use the users set configurations. That's why we are currently spawning an NPM child process. So you need to have NPM installed globally and set in your path. The added benefit of this is that the installation becomes completely silent as NPM is usually really chatty and last but not least, it already works as this module is installed through NPM.

Once it's finally installed it attempts to require it again, if it succeeds it will call your callback without any error arguments and provide the library in the callback. If the installation failed or it failed to require you're basically fucked.

API

package.json example

In the example below, we install canihaz as dependency, and have all our optional dependencies in the property canihaz which will be read out by module.

{
    "name": "example"
  , "description": "example description"
  , "version": "0.0.0"
  , "dependencies": {
        "canihaz": "0.0.x"
    }
  , "canihaz": {
        "coffee-script": "1.3.3"
      , "csslint": "0.9.8"
      , "jshint": "0.7.1"
      , "socket.io": "0.9.6"
      , "stylus": "0.27.2"
      , "watch": "0.5.1"
    }
}

configuration

• dot: Should we create a special dot folder for storage? This is saved in the home directory of the user. Should be a string.
• home: The location of the home folders, as this is operating system specific or you might want to override this if you want to store the dot folder in a different location. Should be string.
• location: The location of the package.json that we need to parse and read out the possible dependencies for lazy installation.
• key: Which property should we scan for the optional dependencies? This allows you to also lazy install optionalDependencies for example.
• installation: The installation location, this is where the dependencies will be installed. It defaults to the package.json folder.

Example:

var canihaz = require('canihaz')({
    key: 'cliDependencies' // read out `cliDependencies` instead of `canihaz`
});

installing/requiring a configured dependency

The dependencies that you specify in the package.json are automatically introduced to the returned export. It assumes that it's loaded by the package that we specified above.

var canihaz = require('canihaz')();

canihaz.jshint(function loading(err, jshint) {
  // jshint is now loaded, unless we got an error
});

installing/requiring a un-configured dependency

Installing or requiring a dependency that isn't in the package.json require direct usage of the API:

var canihaz = require('canihaz')();

canihaz('jshint', '0.7.x', function lazyloading(err, jsint) {
  // jsint is installed with the specified version
});

installing/requiring multiple dependencies

Sometimes you just need a load of modules. There are 2 different ways this is done, if the modules are defined in the package.json it will automatically use their specified function and doesn't require you to specify the version numbers:

var canihaz = require('canihaz')();

canihaz(
    'jshint', 'stylus', 'express'
  , function lazyloading(err, jsint, stylus, express) {
      // the modules are loaded or installed in the same order as the arguments
    }
);

If you need to a bunch of modules that are not specified in the package.

canihaz(
    { name: 'jshint', version: '0.7.x' }
  , { name: 'stylus', version: '' }
  , { name: 'express', version: '3.0.x' }
  , function lazyloading(err, jsint, stylus, express) {
      // the modules are loaded or installed in the same order as the arguments
    }
);

Changelog

1.0.0 Rewritten to use the npm binary for all installations because the programatically API causes to much issues and edge cases. 1.0.0 also features a full test suite and a reworked more powerful API.

all other version were crap anyways

License (MIT)

Copyright (c) 2013 Arnout Kazemier, 3rd-Eden.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.