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Contributing

If you find a bug in the code or a mistake in the documentation or want a new feature, you can help us by creating an issue to our repository, or even better, submit a pull request.

  • For small fixes, please feel free to submit a pull request. Don't worry about creating an issue first.

  • For major changes, please discuss with us via our mailing list and Github first, so we can better coordinate our efforts, prevent duplication of work, and help you to craft the change so that it is successfully accepted into the project.

    • One way to use GitHub for this purpose is to submit a pull request (PR) with a "[WIP]" prefix in the PR's title. With a WIP PR, you can annotate your modification with questions.

  • Generally we name a branch using this pattern <your 2-3 letters initial>/<topic>. For example, @kanitw's branch regarding scale type might be called kw/scale-type.

See our issue and pull request templates for more information.

Looking for a Task to Contribute

You can find tasks with the "Help wanted" label in the issue tracker. Please get in touch if you are planning to work on a major task.

Help Create New Examples

To submit a new example, fork our example Block and send us a pull request to add a link to it to our example gallery.

Documentation and Website

The website is under site/ and the documentation is under site/docs/. We use Github Pages to publish our documentation when we release a new version. To contribute changes to the documentation or website, simply submit a pull request that changes the corresponding markdown files in site/.

The images that are shown on the homepage and in the gallery have to be generated with npm run build:images. To run the script, you need to install gnu parallel. (For Mac, you can simply do brew install parallel.)

Since we only publish the Github Pages when we release a new version, it might be slightly outdated compared to master. For development, once you have setup the repository, you can run yarn site to serve the github page locally at http://localhost:4000/vega-lite/.

Note that when you checkout different branches, the compiled JavaScript for the website might be reset. You will have to run yarn build:site to recompile the JavaScript so that interactive examples work.

Documentation Guide

General Guides for Markdown Files:

  • Wrap properties (key) with back ticks.
  • Wrap values with back ticks for numbers and booleans (e.g., 5, true) and wrap string values with both back ticks and double quotes ("red").

Property Table

To generate a property tables from the JSON schema (which is in turn generated from the Typescript interfaces, you can include the table.html template. For example, to generate a table that includes rangeStep, scheme, and padding from Scale, you can use

{% include table.html props="rangeStep,scheme,padding" source="Scale" %}

To define a link for types in the table, you can edit _data/link.yml.

For JSDocs comment in the interfaces, please add __Default value:__ line at the end to describe the property's value.

Examples

To include an example specification in the documentation, the specification's .vl.json file must be in examples/specs. Then you can use the following span tag to include the specification (e.g., for point_1d.vl.json):

<span class="vl-example" data-name="point_1d"></span>

Before adding a new example, you might want to search inside examples/ folder to see if there are other redundant examples that you can reuse.

To name the example file:

  • Please begin with mark type and follow by some description for a static single view example. For stacked marks, add stacked_ prefix.
  • For composite views, please begin the file with the operator name (e.g., layer).
  • For interactive example, begin with either interactive_ or selection_.
  • For examples that are only for regression test, begin with test_.

After adding a new example, make sure to run yarn build:example <examplename> (e.g., yarn build:example bar_1d) or yarn build:examples to recompile all examples so that your pull request includes a new compiled Vega specs and SVG files in examples/compiled.

Development Guide

Repository Setup

  1. Make sure you have node.js. For mac users, we recommend using homebrew and simply run:
brew install node
  1. Clone this repository and cd into your local clone of the repository, and install all the npm dependencies. We use yarn to have reproducible dependencies:
git clone https://github.com/vega/vega-lite.git
cd vega-lite
yarn

Now you should be able to build and test the code.

  1. To serve the website and documentation, you will need ruby, bundler and Jekyll.

For ruby, Mac users can use homebrew to add it:

brew install ruby@2.3

For bundler:

gem install bundler

For jekyll and its dependencies, because we already have the Gemfile in the repo, you can simply run:

bundle install

Directory Structure

  • _layouts/ – Our website and documentation's Jekyll layout files.

  • bin/ – Scripts for using Vega-Lite with command line.

  • data/ – Example data.

  • site/ – Vega-Lite website including documentation.

  • examples/ – Example Vega-Lite specifications.

    • specs Vega-Lite examples.
    • compiled The generated Vega specifications and SVG files of the Vega-Lite examples.

  • scripts/ - Scripts for NPM commands.

  • site/ - Misc files for serving the website and gallery.

  • src/ - Main source code directory.

    • All interfaces for Vega-Lite syntax should be declared at the top-level of the src/ folder.
      • src/index.ts is the root file for Vega-Lite codebase that exports the global vl object.
      • Other files under src/ reflect namespace structure. All methods for vl.xxx will be in either src/xxx.ts or src/xxx/xxx.ts. For example, vl.channel.* methods are in src/channel.ts while vl.compile is in src/compile/compile.ts.

  • test/ - Code for unit testing. test's structure reflects src's directory structure. For example, test/compile/ tests files inside src/compile/.

    • Note that we prepend /* tslint:disable:quotemark */ to all files under test/compile to allow putting JSON specs in tests directly without getting lint errors.

  • typings/ - TypeScript typing declaration for dependencies.

Understanding How Vega-Lite Works

  • The main compiler code is in src/compile/compile.ts. To try to understand how Vega-Lite works, first start by reading the compile method in the file and try to understand different phases in the compilation process.

Commands

This section lists commands that are commonly used during development. See package.json for other commands.

Build

You can run npm run build to compile Vega-Lite and regenerate vega-lite-schema.json.

Basic Lint & Test & Test Coverage

npm run lint and npm run test run ts-lint and all unit-tests respectively. These two commands are automatically run by npm start and npm run watch.

npm run test includes test coverage and generates a report inside coverage/index.html. You can see if specific lines are covered in the unit test by running open coverage/index.html and browsing through the report.

A lot of linting errors can be fixed automatically by running npm run lint --fix.

Watch tasks

During development, it can be convenient to rebuild automatically or to run tests in the background.

npm run start starts a watcher task that shows the example gallery. Whenever any .ts file changes, the watcher: (1) re-compiles Vega-Lite (2) automatically refreshes the gallery with BrowserSync (3) lints and runs tests (4) regenerates the JSON schema (vega-lite-schema.json).

If you only want subset of these actions, you can use:

  • npm run watch to start a watcher task that does all of above except opening and syncing the gallery.

  • npm run watch:test to start a watcher task that lints and runs tests when any .ts file changes.

  • npm run watch:build to start a watcher task that re-compiles Vega-Lite when .ts files related to VL change.

Fast iteration testing

To quickly run tests without long compile times, run npm run tsc -w in a separate terminal session. Then run npm run mocha:test to quickly run tests (or npm run mocha:test --inspect --debug-brk to inspect tests). Please note that this only runs unit tests; you should run the full tests before committing code.

Website

npm run site. See details in Documentation and Website.

Deployment

(For team members only) npm run deploy will publish latest code to NPM and Bower and also update github pages, which contains our webpage and documentation. If you want to update only github pages, use npm run deploy:gh.

Suggested Programming Environment.

We use the Visual Studio Code editor with TSLint plugin.

  • VSCode has nice built-in Typescript support!
  • We already include project settings to hide compiled files (*.js, *.js.map). This should work automatically if you open the vega-lite folder with VSCode.
  • Make sure to install TypeScript Importer and TSLint extensions.

Manually Testing with Vega-Editor

To manually test your changes locally, you should have a local instance of Vega Editor and link Vega-Lite to the editor (See Vega Editor's README for instructions).

Developing Vega-Lite and Vega-Util

Vega-Lite depends on vega-util. If you plan to make changes to the utils and test Vega-Lite without publishing / copying compiled vega-util all the time, use npm link.

# first link vega-util global npm
cd path/to/vega-util
npm link
# then link vega-lite to datalib
cd path/to/vega-lite
npm link vega-util

Now all of the changes you make in vega-util are reflected in your Vega-Lite automatically.

Pull Requests and Travis

All pull requests will be tested on Travis. If your PR does not pass the checks, your PR will not be approved. Travis' environments will run npm run test, generate vega specs and SVG files from your updated code, compare them with the existing compiled outputs in examples/compiled/, and check code coverage of your code. (See .travis.yml for the commands it executes.) If you don't want your PR reviewed until Travis checks pass, just prepend [WIP] to the title of your PR. Once you're ready for review, remove the [WIP] prefix and comment that the PR is ready for review.

Code Coverage

When checking for code coverage, we require that your PR tests cover at least the same percentage of code that was being covered before. To check the code coverage, you can see the link in the job log of your Travis test, from the Github page of your PR, or on https://codecov.io/gh/vega/vega-lite/commits. It'll be usually in the form of https://codecov.io/gh/vega/vega-lite/commit/your-full-head-commit-number. Under the Files and Diff tab, you can check your code coverage differences and total. In Files, you can check which lines in your files are being tested (marked in green) and which are not (marked in red). We appreciate PRs that improve our overall code coverage!

Note

Vega-Lite enables a number of open-source applications including user interface tools (PoleStar and Voyager) and visualization recommender (Compass). Look at their contribute pages if you are interested!

Acknowledgment: This contribution guide is partly inspired by angular.js's CONTRIBUTION.md.