Completion library for CLI commands

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1.0.33 years ago11 years agoMinified + gzip package size for completion in KB


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
        - If no `completion` is specified, we assume this is terminal and stop recursing
        - More info is available in the [`commands/option completion` section][command-completion-section]
- 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
    - More info is available in the [`commands/option completion` section][command-completion-section]

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 methodshift-left-word.
For completing partial matches, we provide the matchLeftWord methodmatch-left-word.
To create non-terminal options, we can use the method resolveInforesolve-info 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
- This is converted from `params` to its current equivalent 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.