detectionizr

Detect npm modules and system libraries with the same ease as Modernizr. Never has feature detection in Node.js been so easy!

Getting Started

Install the module with: npm install detectionizr

The one liner:

var d = require('detectionizr').detect(['html-doc', 'html-md']) // that's it!

Now you could do this:

d['html-doc'] ?                   // is html-doc available?
  d['html-doc'].parse(markdown) : // then use it
    d['html-md'] ?                // if not, is html-md available?
      d['html-md'].md(markdown) : // then use it
      console.error("No markdown support")  // both d['html-doc'] and d['html-md'] are false

var detectionizr = require('detectionizr');
// be sure to attach event handler before you use detect
test.on("detect", function(name, exist) {
  if(name === "ls" && test.ls)
    console.log("We can use ls on this computer!");
});
// call detect with an array of commands you want to test for
test.detect(["imagemagick", "ls", "punycode"]);
 
if(test.punycode)
  console.log("We can use test.punycode");
if(test.imagemagick)
  console.log("We can use test.imagemagick");

Documentation

I use command, system library and nodejs module interchangeably in this text.

NOT TESTED ON WINDOWS

detectionizr has 4 methods:

• require ({String}) - works like the normal require, except false is returned if the module can not be found
• detect ({Array}) - takes a list of command names to test and grows your detectionizr variable with references to the commands. Note, that command line commands will not be available right away. See below.
• on ({String}, {Function}, [{Object}]) - If a command is not a node module, then the test run asynchronously, and you have to attach an event listener. In the current version, "detect" and "finally" is accepted as event name. The second argument is your callback function and the third (optional) the scope you want your callback to run in. The listener will be called with 2 arguments, the name {String} and if it could be found {Boolean}. Multiple event listeners can be attached. All "detect" listeners are called for each package you are testing.
• overwrite ({String}, {Function}, [{Object}]) - The same as on but will delete all previous attached "detect" listeners.

Eat your own dog food

detectionizr uses child_process from native nodejs modules and also checks in the same manner as it will test your library dependecies. That is why, detectionizr will always have a reference to child_process.

How this works

detectionizr will first try and require the commands. If that fails, it will search for the command as a process with: command -v [command name], which and whereis and look for a return value. If you experience false positives, please file a bug in the issue tracker. The command command should be available on all POSIX compliant systems (OS X, Linux, Unix ect.). which and whereis should be able to find libraries like g++ ect.

Examples

var test = require("detectionizr");
function PackageManager() {
    this.available = [];
}
PackageManager.prototype.recieve = function(name, exist) {
    if(exist) this.available.push(name)
}
var pm = new PackageManager();
test.on("detect", pm.recieve, pm);
test.on("finally", function() {
  console.dir(pm);    // { available: [ 'imagemagick', 'rdjpgcom' ] }
  console.dir(test);  /* { child_process: 
                           { fork: [Function],
                             _forkChild: [Function],
                             exec: [Function],
                             execFile: [Function],
                             spawn: [Function] },
                          require: [Function: r],
                          detect: [Function],
                          on: [Function],
                          overwrite: [Function],
                          rdjpgcom: true, <- command line libraries can not be referenced
                          imagemagick: <- but nodejs modules are referenced
                           { identify: { [Function] path: 'identify' },
                             readMetadata: [Function],
                             convert: { [Function] path: 'convert' },
                             resize: [Function],
                             crop: [Function],
                             resizeArgs: [Function] },
                          imgcheck: false }*/
});
test.detect(["rdjpgcom", "imagemagick", "imgcheck"]);

// Instead of
var mongodb;
try {
    mongodb = require( 'mongodb' );
}
catch( e ) {
    if ( e.code === 'MODULE_NOT_FOUND' ) {
        // The module hasn't been found
    }
}
 
// write
if( !require('detectionizr').detect(['mongodb']).mongodb) )
    // The module hasn't been found
 
// or
var mongodb = require('detectionizr').detect(['mongodb'].mongodb;
if(!mongodb)
  // The module hasn't been found
// if you need to do something with mongodb later

TODO

• Implement dereferencing with delete http://nodejs.org/docs/latest/api/globals.html#globals_require_cache
• Better documentation...
• Better tests...

Contributing

In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Test your code using grunt. NOTE - If you symlink detectionizr into a another folder, e.g. npm link [../path/to/detectionizr], detectionizr will not be able to find modules in that folder's node_modules directory. This is because nodejs require function only looks in the symlinked folder and not in the folder you are working in. See issue #4757.

Release History

• 0.1.5 - For some reason the 0.1.4 release didn't remove whereis as a test program. This was what the 0.1.4 release was suppose to do. Sorry.
• 0.1.4 - Fixed false positives on ubuntu. Bug #1
• 0.1.3 - Added "finally" event and fixed various bugs. detectionizr is now chainable.
• 0.1.2 - .detect now return a reference to detectionizr. Enabling the one liner.
• 0.1.1 - Fix for event listeners not being called for nodejs modules.
• 0.1.0 - Initial release

License

Copyright (c) 2013 dotnetCarpenter Licensed under the WTFPL license.