For development tasks such as contributing, running benchmarks or testing, you need to clone the repository and install dev-dependencies.

Install node

git clone
cd bluebird
npm install

Directory structure

  • /benchmark contains benchmark scripts and stats of benchmarks

  • /tools contains building and testing tools and scripts

  • /src contains the source code

  • /test contains test code

    • /test/mocha contains tests using the mocha testing framework
    • /test/browser a directory that can be statically served using a webserver to run tests in browsers. See testing in browsers.

Style guide

Use the same style as is used in the surrounding code.


  • No more than 80 columns per line
  • 4 space indentation
  • No trailing whitespace
  • LF at end of files
  • Curly braces can be left out of single statement if/else/else ifs when it is obvious there will never be multiple statements such as null check at the top of a function for an early return.
  • Add an additional new line between logical sections of code.


  • Use multiple var statements instead of a single one with comma separator. Do not declare variables until you need them.

Equality and type checks

  • Always use === except when checking for null or undefined. To check for null or undefined, use x == null.
  • For checks that can be done with typeof: do not make helper functions, save results of typeof to a variable or make the type string a non-constant. Always write the check in the form typeof expression === "constant string" even if it feels like repeating yourself.


node tools/build --debug --release --zalgo --browser --minify

Supported options by the build tool

The value of boolean flags is determined by presence, if you want to pass false value for a boolean flag, use the no--prefix e.g. --no-debug.

  • --release - Whether to build the release build. The release build is placed at js/release directory. Default false.
  • --debug - Whether to build the debug build. The debug build is placed at js/debug directory. Default false.
  • --zalgo - Whether to build the zalgo build. The zalgo build is placed at js/zalgo directory. Default false.
  • --browser - Whether to compile the browser build. The browser build file is placed at js/browser/bluebird.js Default false.
  • --minify - Whether to minify the compiled browser build. The minified browser build file is placed at js/browser/bluebird.min.js Default true.


To run all tests, run

node --expose-gc tools/test

If you need to run generator tests in older versions of NodeJS run the tool/test.js script with --harmony argument and 0.11+:

node-dev --harmony tools/test

In recent versions of NodeJS where generators are enabled by default:

node tools/test

You may specify an individual test file to run with the --run script flag:

node tools/test --run=cancel.js

This enables output from the test and may give a better idea where the test is failing. The paramter to --run can be any file name located in test/mocha folder.

Testing in browsers

To run the test in a browser instead of node, pass the flag --browser to the test tool

node tools/test --run=cancel.js --browser

This will automatically create a server (default port 9999) and open it in your default browser once the tests have been compiled.

Keep the test tab active because some tests are timing-sensitive and will fail if the browser is throttling timeouts. Chrome will do this for example when the tab is not active.

Supported options by the test tool

The value of boolean flags is determined by presence, if you want to pass false value for a boolean flag, use the no--prefix e.g. --no-browser.

  • --run=String. Which tests to run (or compile when testing in browser). Default "all". Can also be a glob string (relative to ./test/mocha folder)
  • --cover=String. Create code coverage using the String as istanbul reporter. Coverage is created in the ./coverage folder. No coverage is created by default, default reporter is "html" (use --cover to use default reporter).
  • --browser - Whether to compile tests for browsers. Default false.
  • --port=Number - Whe port where local server is hosted when testing in browser. Default 9999
  • --execute-browser-tests - Whether to execute the compiled tests for browser when using --browser. Default true.
  • --open-browser - Whether to open the default browser when executing browser tests. Default true.
  • --fake-timers - Whether to use fake timers (setTimeout etc) when running tests in node. Default true.
  • --js-hint - Whether to run JSHint on source files. Default true.
  • --saucelabs Wheter to create a tunnel to sauce labs and run tests in their VMs instead of your browser when compiling tests for browser.Default false.


To run a benchmark, run the given command for a benchmark while on the project root. Requires bash (on windows the mingw32 that comes with git works fine too).

Each benchmark must

  • Have implementations that do the same thing
  • Run each implementation of a benchmark in a separate freshly created process
  • Warmup each implementation before timing

1. DoxBee sequential

Currently the most relevant benchmark is @gorkikosev's benchmark in the article Analysis of generators and other async patterns in node. The benchmark emulates a situation where n amount of users are making a request in parallel to execute some mixed async/sync action.

Command: bench doxbee

The implementations for this benchmark are found in benchmark/doxbee-sequential directory.

2. Parallel

This made-up scenario runs 25 shimmed queries in parallel.

Command: bench parallel

The implementations for this benchmark are found in benchmark/madeup-parallel directory.