<p align="center">
  <a href="http://liftoffjs.com">
    <img height="100" width="297" src="https://cdn.rawgit.com/tkellen/js-liftoff/master/artwork/liftoff.svg"/>
  </a>
</p>

# liftoff [![Build Status](https://secure.travis-ci.org/js-cli/js-liftoff.svg)](http://travis-ci.org/js-cli/js-liftoff) [![Build status](https://ci.appveyor.com/api/projects/status/5a6w8xuq8ed1ilc4/branch/master?svg=true)](https://ci.appveyor.com/project/js-cli/js-liftoff/branch/master)

> Launch your command line tool with ease.

[![NPM](https://nodei.co/npm/liftoff.png)](https://nodei.co/npm/liftoff/)

## What is it?
[See this blog post](http://weblog.bocoup.com/building-command-line-tools-in-node-with-liftoff/), [check out this proof of concept](https://github.com/js-cli/js-hacker), or read on.

Say you're writing a CLI tool.  Let's call it [hacker](https://github.com/js-cli/js-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`&mdash;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:
```js
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:
```js
const Hacker = Liftoff({
  processTitle: 'hacker',
  moduleName: 'hacker',
  configName: 'hackerfile'
});
```
```js
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.
```js
const MyApp = new Liftoff({
  name: 'myapp',
  extensions: {
    '.js': null,
    '.json': null,
    '.coffee': 'coffee-script/register'
  }
});
```

In this example, Liftoff will look for `.myapp{rc}`.
```js
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](https://github.com/tkellen/node-interpret) (as long as it does not require a register method).

```js
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](http://github.com/tkellen/node-flagged-respawn). To support all v8flags, see [node-v8flags](https://github.com/tkellen/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](http://nodejs.org/api/process.html#process_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:
```js
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:**
```js
const argv = require('minimist')(process.argv.slice(2));
MyApp.launch({
  cwd: argv.cwd
}, invoke);
```

**Matching CLI Invocation:**
```
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:**
```js
var argv = require('minimist')(process.argv.slice(2));
MyApp.launch({
  configPath: argv.myappfile
}, invoke);
```

**Matching CLI Invocation:**
```
myapp --myappfile /var/www/project/Myappfile.js
```

**Examples using `cwd` and `configPath` together:**

These are functionally identical:
```
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:
```
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:**
```js
var argv = require('minimist')(process.argv.slice(2));
MyApp.launch({
  require: argv.require
}, invoke);
```

**Matching CLI Invocation:**
```js
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.

```js
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.

```js
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`](#optsnodeflags) is detected).

```js
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](https://github.com/gulpjs/gulp/blob/master/bin/gulp.js) uses Liftoff.

For a bare-bones example, try [the hacker project](https://github.com/js-cli/js-hacker/blob/master/bin/hacker.js).

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`.
3. Run `hacker` while in the same parent folder.
