liftoff

Launch your command line tool with ease.

What is it?

See this blog post, check out this proof of concept, or read on.

Say you're writing a CLI tool. Let's call it hacker. You want to configure it using a Hackerfile. This is node, so you install hacker locally for each project you use it in. But, in order to get the hacker command in your PATH, you also install it globally.

Now, when you run hacker, you want to configure what it does using the Hackerfile in your current directory, and you want it to execute using the local installation of your tool. Also, it'd be nice if the hacker command was smart enough to traverse up your folders until it finds a Hackerfile—for those times when you're not in the root directory of your project. Heck, you might even want to launch hacker from a folder outside of your project by manually specifying a working directory. Liftoff manages this for you.

So, everything is working great. Now you can find your local hacker and Hackerfile with ease. Unfortunately, it turns out you've authored your Hackerfile in coffee-script, or some other JS variant. In order to support that, you have to load the compiler for it, and then register the extension for it with node. Good news, Liftoff can do that, and a whole lot more, too.

API

constructor(opts)

Create an instance of Liftoff to invoke your application.

An example utilizing all options:

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const Hacker = new Liftoff({
  name: 'hacker',
  processTitle: 'hacker',
  moduleName: 'hacker',
  configName: 'hackerfile',
  extensions: {
    '.js': null,
    '.json': null,
    '.coffee': 'coffee-script/register'
  },
  v8flags: ['--harmony'] // or v8flags: require('v8flags');
});

opts.name

Sugar for setting processTitle, moduleName, configName automatically.

Type: String
Default: null

These are equivalent:

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const Hacker = Liftoff({
  processTitle: 'hacker',
  moduleName: 'hacker',
  configName: 'hackerfile'
});

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const Hacker = Liftoff({name:'hacker'});

opts.moduleName

Sets which module your application expects to find locally when being run.

Type: String
Default: null

opts.configName

Sets the name of the configuration file Liftoff will attempt to find. Case-insensitive.

Type: String
Default: null

opts.extensions

Set extensions to include when searching for a configuration file. If an external module is needed to load a given extension (e.g. .coffee), the module name should be specified as the value for the key.

Type: Object
Default: {".js":null,".json":null}

Examples:

In this example Liftoff will look for myappfile{.js,.json,.coffee}. If a config with the extension .coffee is found, Liftoff will try to require coffee-script/require from the current working directory.

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const MyApp = new Liftoff({
  name: 'myapp'
  extensions: {
    '.js': null,
    '.json': null,
    '.coffee': 'coffee-script/register'
  }
});

In this example, Liftoff will look for .myapp{rc}.

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const MyApp = new Liftoff({
  name: 'myapp',
  configName: '.myapp',
  extensions: {
    'rc': null
  }
});

In this example, Liftoff will automatically attempt to load the correct module for any javascript variant supported by node-interpret (as long as it does not require a register method).

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const MyApp = new Liftoff({
  name: 'myapp',
  extensions: require('interpret').jsVariants
});

opts.v8flags

Any flag specified here will be applied to node, not your program. Useful for supporting invocations like myapp --harmony command, where --harmony should be passed to node, not your program. This functionality is implemented using flagged-respawn. To support all v8flags, see node-v8flags.

Type: Array|Function
Default: null

If this method is a function, it should take a node-style callback that yields an array of flags.

opts.processTitle

Sets what the process title will be.

Type: String
Default: null

opts.completions(type)

A method to handle bash/zsh/whatever completions.

Type: Function
Default: null

launch(opts, callback(env))

Launches your application with provided options, builds an environment, and invokes your callback, passing the calculated environment as the first argument.

Example Configuration w/ Options Parsing:

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const Liftoff = require('liftoff');
const MyApp = new Liftoff({name:'myapp'});
const argv = require('minimist')(process.argv.slice(2));
const invoke = function (env) {
  console.log('my environment is:', env);
  console.log('my cli options are:', argv);
  console.log('my liftoff config is:', this);
};
MyApp.launch({
  cwd: argv.cwd,
  configPath: argv.myappfile,
  require: argv.require,
  completion: argv.completion
}, invoke);

opts.cwd

Change the current working directory for this launch. Relative paths are calculated against process.cwd().

Type: String
Default: process.cwd()

Example Configuration:

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const argv = require('minimist')(process.argv.slice(2));
MyApp.launch({
  cwd: argv.cwd
}, invoke);

Matching CLI Invocation:

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myapp --cwd /

opts.configPath

Don't search for a config, use the one provided. Note: Liftoff will assume the current working directory is the directory containing the config file unless an alternate location is explicitly specified using cwd.

Type: String
Default: null

Example Configuration:

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var argv = require('minimist')(process.argv.slice(2));
MyApp.launch({
  configPath: argv.myappfile
}, invoke);

Matching CLI Invocation:

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myapp --myappfile /var/www/project/Myappfile.js

Examples using cwd and configPath together:

These are functionally identical:

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myapp --myappfile /var/www/project/Myappfile.js
myapp --cwd /var/www/project

These can run myapp from a shared directory as though it were located in another project:

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myapp --myappfile /Users/name/Myappfile.js --cwd /var/www/project1
myapp --myappfile /Users/name/Myappfile.js --cwd /var/www/project2

opts.require

A string or array of modules to attempt requiring from the local working directory before invoking the launch callback.

Type: String|Array
Default: null

Example Configuration:

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var argv = require('minimist')(process.argv.slice(2));
MyApp.launch({
  require: argv.require
}, invoke);

Matching CLI Invocation:

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myapp --require coffee-script/register

callback(env)

A function to start your application. When invoked, this will be your instance of Liftoff. The env param will contain the following keys:

• cwd: the current working directory
• require: an array of modules that liftoff tried to pre-load
• configNameSearch: the config files searched for
• configPath: the full path to your configuration file (if found)
• configBase: the base directory of your configuration file (if found)
• modulePath: the full path to the local module your project relies on (if found)
• modulePackage: the contents of the local module's package.json (if found)

events

require(name, module)

Emitted when a module is pre-loaded.

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var Hacker = new Liftoff({name:'hacker'});
Hacker.on('require', function (name, module) {
  console.log('Requiring external module: '+name+'...');
  // automatically register coffee-script extensions
  if (name === 'coffee-script') {
    module.register();
  }
});

requireFail(name, err)

Emitted when a requested module cannot be preloaded.

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var Hacker = new Liftoff({name:'hacker'});
Hacker.on('requireFail', function (name, err) {
  console.log('Unable to load:', name, err);
});

respawn(flags, child)

Emitted when Liftoff re-spawns your process (when a nodeFlag is detected).

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var Hacker = new Liftoff({
  name: 'hacker',
  nodeFlags: ['--harmony']
});
Hacker.on('respawn', function (flags, child) {
  console.log('Detected node flags:', flags);
  console.log('Respawned to PID:', child.pid);
});

Event will be triggered for this command: hacker --harmony commmand

Examples

Check out how gulp uses Liftoff.

For a bare-bones example, try the hacker project.

To try the example, do the following:

1. Install the sample project hacker with npm install -g hacker.
2. Make a Hackerfile.js with some arbitrary javascript it.
3. Install hacker next to it with npm install hacker.
4. Run hacker while in the same parent folder.