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completion Build status

Completion library for CLI commands

This was built as part of foundry, a CLI utility for making releases painless.

$ git chec|
$ git checkout |

$ git checkout dev/|
dev/ dev/goodbye.moon

$ git chec|dev/
$ git checkout |dev/

Getting Started

Install the module with: npm install completion

var Completion = require('completion');
var completion = new Completion({
  name: 'git',
  commands: [{
    name: 'checkout',
    completion: function (info, cb) {
      // For `git checkout dev/|`
      // info.words.value = ['git', 'checkout', 'dev/']
      // info.word.partialLeft = 'dev/'
      var that = this;
      getGitBranches(function (err, allBranches) {
        if (err) {
          return cb(err);

        // Match 'dev/' === 'dev/' (from 'dev/hello')
        var partialLeftWord = info.word.partialLeft;
        var branches = that.matchLeftWord(partialLeftWord, allBranches);
        cb(null, branches);
  // `git chec|`
  line: 'git chec',
  cursor: 8
}, function (err, results) {
  results; // ['checkout']

How it works

In bash, tab completion will override the the left half of the current word.

As a result, for cases like:

$ git chec|
$ git checkout| # requires ['checkout'] to be returned

Unfortunately, while we can deal with commands, we cannot predict the values of those.

You will still be responsible for handling of right partials in the autocompleted items.

$ git checkout a|c
  'abc', # `git checkout abc` - Checkout `abc` branch
  'aaa' # `git checkout aaa c` - Chekckout `c` file from `aaa` branch


completion exposes the Completion constructor via its module.exports

new Completion(tree)

Create a new completion instance

  • tree Object - Outline of a program/command
    • name String - Command that is being executed (e.g. git, checkout)
    • options Object[] - Optional array of objects that represent options
      • name String - Name of option (e.g. --help)
      • completion Function - Optional function to complete the remainder of the invocation
    • commands Object[] - Optional array of new tree instances to complete against
      • This cannot exist on the same node as completion as they are contradictory
    • completion Function - Optional completion function to determine results for a command

completion.complete(params, cb)

Get potential completion matches for given parameters

  • params Object - Information similar to that passed in by bash's tab completion
    • line String - Input to complete against (similar to COMP_LINE)
    • cursor Number - Index within line of the cursor (similar to COMP_POINT)
  • cb Function - Error-first callback function that receives matches
    • cb should have a signature of function (err, results)

command/option completion functions

options and commands share a common completion function signature, function (info, cb)

Each completion function will be executed with the command node as its this context

  • info Object - Information about original input
    • Content will be information from twolfson/line-info
    • We provide 2 additional properties
      • words.matchedLeft String[] - Words matched from words.partialLeft while walking the tree
      • words.remainingLeft String[] - Unmatched words that need to be/can be matched against
  • cb Function - Error-first callback function to return matches via
    • cb has a signature of function (err, results)

For options, it is often preferred to remove more words that are matched (e.g. -m <msg>). For this, we suggest using the shiftLeftWord method.

For completing partial matches, we provide the matchLeftWord method.

To create non-terminal options, we can use the method resolveInfo to keep on searching against the remainingLeft words.


Helper function to shift word from info.words.remainingLeft to info.words.matchedLeft

  • info Object - Information passed into completion functon
var info = {words: {remainingLeft: ['hello', 'world'], matchedLeft: []}};
info = this.shiftLeftWord(info);
info; // {words: {remainingLeft: ['world'], matchedLeft: ['hello']}}

completion.matchLeftWord(leftWord, words)

Helper function to find words from words that start with leftWord

  • leftWord String - Word to match left content of
    • leftWord gets its name from usually coming from words.partialLeft
  • words String[] - Array of words to filter against


  • matchedWords String[] - Matching words from words that start with leftWord
this.matchLeftWord('hello', ['hello-world', 'hello-there', 'goodbye-moon']);
// ['hello-world', 'hello-there'];

completion.resolveInfo(info, cb)

Recursively find matches against the Completion's tree with a given info

  • info Object - CLI information provided by twolfson/line-info
  • cb Function - Error first callback function that receives matches
    • cb should be the same as in completion.complete


An example of git would be

var gitCompletion = new Completion({
  name: 'git',
  options: [{
    // `git --help`, a terminal option
    name: '--help'
  commands: [{
    // `git checkout master`
    name: 'checkout',
    option: [{
      // `git checkout -b dev/hello`
      name: '-b',
      completion: function (info, cb) {
        // `-b` was matched by `completion` so keep on recursing
        return this.resolveInfo(info, cb);
    completion: function getGitBranches (info, cb) {
      // Get git branches and find matches
  }, {
    name: 'remote',
    commands: [{
      // `git remote add origin`
      // No possible completion here
      name: 'add'
    }, {
      // `git remote rm origin`
      name: 'rm',
      completion: function getGitBranches (info, cb) {
        // Get git branches and find matches

  // `git remo|add`
  line: 'git remoadd',
  cursor: 8
}, function (err, results) {
  results; // ['remote']

  // `git remote |`
  line: 'git remote ',
  cursor: 11
}, function (err, results) {
  results; // ['add', 'remove']


In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint via grunt and test via npm test.


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As of Dec 15 2013, Todd Wolfson has released this repository and its contents to the public domain.

It has been released under the UNLICENSE.

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