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0.0.6 • Public • Published


JavaScript Task Runner that's easily configured to run complex sequences of tasks.

The underlying engine is bit loader to provide the transformation workflow.


bit runner's primary goal is to execute tasks, and the engine that executes these tasks is optimized to reduce I/O operations by piping data from one task to another.

So, what is a task? A task is a list of actions that are executed in sequence to process your assets. You define these actions in the form of plugins or functions. An action can be to simply add use strict; to your JavaScript.

A task can also specify dependencies on other tasks. This allows you to define a uniform task sequence that executes as a single unit, where the output from one task is piped to the next task in the sequence to reduce unnecessary I/O.

An important feature of the ability to set task dependencies is that you can piece together sequences of micro tasks to build complex pipelines - micro tasks are tasks that do small jobs.

When bit runner executes a task sequence, it runs completely independent from other task sequences. For example, if you tell bit runner to execute a task called build and to also execute release simultaneously, they will both run in isolation, even if they have common task dependencies. This allows for elegant compositions of sequences of micro tasks.

Task sequences run in isolation.

Quick note: A task is what bit runner executes. Actions is what a task executes. Bit runner executes a sequence of tasks, and a task executes a sequence of actions.

Oversimplified illustration of a task sequence

  • Task: read from disk
    • Action: read file1.js
  • Task: transpile
  • Task: build
    • Action: add use strict
    • Action: add # sourceURL
    • Action: load dependencies
  • Task: minify

In all that sequence, there was only one read from disk!



You need to install bit-runner globally so that the bit-runner cli can be added to the PATH. This way you can call bitrunner from anywhere to execute your tasks.

npm install bit-runner -g

Now that you have the cli in your PATH, you need to install bit-runner in your project in order for your bit runner configuration to register tasks. So from your project's root directory:

npm install bit-runner --save-dev

Configuration bitrunnerfile.js

When you execute bit runner's cli, it automatically loads bitrunnerfile.js from your project in order to load your tasks. Here is a basic configuration with a single task called build:

var bitRunner = require('bit-runner');
var babel     = require('babel-bits');
 * JavaScript build pipeline
bitRunner.register('build', function buildPipeline(task) {
 * Sample action. The `source` property is generally what actions operate on.
function addStrict(moduleMeta) {
  moduleMeta.source = "'use strict;'\n" + moduleMeta.source;

Running it

So, now that you have installed bit-runner and created a configuration in your project, you are ready to run your task(s). From your project's root directory:

bitrunner build

You can call bitrunner with a list of tasks, in which case bit runner is going to run them in parallel. Or if you don't provide a task name, then the default task is executed.

The following will execute build and docs in parallel.

bitrunner build docs

The following will execute default



Please see examples that illustrate different techniques for configuring bit runner.


You can click here to see a list of bit runner plugins.

Authoring plugins

So, what is a plugin? A plugin is basically a function that is called by bit runner. bit runner passes in data that needs processing to each plugin. In general, the item of interest in the data passed in is the source property. And that's because that's the content that has been loaded from storage.

When writing a plugin, keep in mind the basic rule that plugins are small units of work. Meaning, don't over complicate a plugin by overloading it with functionality that could be otherwise broken out into smaller plugins.

A very basic plugin has the following structure:

function foo(data) {
module.exports = foo;

And you would use it as follows:

var foo = require('foo')
taskRunner.register('default', function(task) {

If you need to provide a way to configure the plugin, the following structure is suggested:

function foo(data) {
  _run(data, {});
foo.config = function(options) {
  return function fooDelegate(data) {
    _run(data, options);
function _run(data, options) {
  // Do what you need to here
  console.log(data, options);
module.exports = foo;

Returning the delegate might seem a bit odd. But it makes the plugin a bit cleaner when it is used.

var foo = require('foo')
taskRunner.register('default', function(task) {
  task.then(foo.config({hello: world}));

You can take a look at this one to get an idea of what a full plugin looks like.

bit runner plugins are actually bit loader transforms. So you can generally use a bit loader transform as a bit runner task action.


npm i bit-runner

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