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Developer Guide

Thank you for your interest in contributing to Perspective! This guide will teach you everything you need to know to get started hacking on the Perspective codebase.

If you're coming to this project as principally a JavaScript developer, please be aware that Perspective is quite a bit more complex than a typical NPM package due to the mixed-language nature of the project; we've done quite a bit to make sure the newcomer experience is as straightforward as possible, but some things might not work the way you're used to!

This guide provides instructions for both the JavaScript and Python libraries. To switch your development toolchain between the two, use yarn setup. Once the setup script has been run, common commands like yarn build and yarn test automatically call the correct build and test tools.

System Dependencies

Perspective.js and perspective-python require the following system dependencies to be installed:

  • CMake (version 3.15.4 or higher)
  • Boost (version 1.67 or higher, must be built - not header-only). This can be installed from tarball with the included script node tools/perspective-scripts/install_tools.mjs.
  • Yarn (v1). Important: Yarn >v1 is not supported, and will cause build errors.

This list may be non-exhaustive depending on your OS/environment; please open a thread in Discussions if you have any questions


Make sure you have the system dependencies installed. For specifics depending on your OS, check the system-specific instructions below.

To run a build, use

yarn build

If this is the first time you've built Perspective, you'll be asked to generate a .perspectiverc via a short survey. This can be later re-configured via

yarn setup

If everything is successful, you should be able to run any of the examples/ packages, e.g. examples/blocks like so:

yarn start blocks


To build the JavaScript library, which includes WebAssembly compilation, Emscripten and its prerequisites are required.

Perspective.js specifies its Emscripten version dependency in package.json, and the correct version of Emscripten will be installed with other JS dependencies by running yarn.

Building via local EMSDK

To build using an Emscripten install on your local system and not the Emscripten bundled with Perspective in its package.json, install the Emscripten SDK, then activate and export the latest emsdk environment via

source emsdk/

Deviating from this specific version of Emscripten specified in the project's package.json can introduce various errors that are extremely difficult to debug.

To install a specific version of Emscripten (e.g. 2.0.6):

./emsdk install 2.0.6


To build the Python library, first configure your project to build Python via yarn setup. Then, install the requirements corresponding to your version of python, e.g.

pip install -r python/perspective/requirements-311.txt

perspective-python supports Python 3.8 and upwards.


To install the Jupyterlab/Jupyter Notebook plugins from your local working directory, simply install python/perspective with pip as you might normally do.

(cd packages/perspective-jupyterlab && yarn run build)
pip install -e python/perspective
jupyter labextension develop python/perspective

Afterwards, you should see it listed as a "local extension" when you run jupyter labextension list and as a normal extension when you run jupyter nbextension list.

As an example, your setup process might look like this:

python -m venv ./venv
pip install -r python/perspective/requirements-311.txt
yarn setup # choose python
yarn build
yarn setup # choose javascript > jupyterlab
yarn build
yarn jlab_link # run this whenever you need to update a local perspective package

System-Specific Instructions


Install system dependencies through Homebrew:

brew install cmake

On M1 (Apple Silicon) systems, make sure your brew-installed dependencies are in /opt/homebrew (the default location), and that /opt/homebrew/bin is on the PATH.

Note: Perspective vendors its C++ extensions, so you may run into trouble building if you have brew-installed versions of libraries, such as flatbuffers.

Windows 10

You need to use bash in order to build Perspective packages. To successfully build on Windows 10, enable Windows Subsystem for Linux (WSL) and install the Linux distribution of your choice.

Create symbolic links to easily access Windows directories and projects modified via Windows. This way, you can modify any of the Perspective files using your favorite editors on Windows and build via Linux.

Follow the Linux specific instructions to install Emscripten and all prerequisite tools.


On Ubuntu, CMake will mistakenly resolve the system headers in /usr/include rather than the emscripten supplied versions. You can resolve this by moving boost dependencies to somewhere other than /usr/include - into Perspective's own src dir (as per here).

apt-get install libboost-all-dev
cp -r /usr/include/boost ./packages/perspective/src/include/


You can run the test suite simply with the standard NPM command, which will both build the test suite for every package and run them.

yarn test [--debug]

A test name regex can be passed to jest via the same -t flag:

yarn test -t 'button test (A|B)'


The JavaScript test suite is composed of two sections: a Node.js test, which asserts behavior of the @finos/perspective library, and a suite of Puppeteer tests, which assert the behavior of the rest of the UI facing packages.

The Puppeteer/UI tests are a form of characterization tests which use screenshots to compare current and previous behavior of <perspective-viewer> and its plugins. The results of each comparison are stored in each package's test/results/results.json file, and the screenshots themselves are stored in the package's tests/screenshots/ directory, though only the former should be checked into GIT. When a test in these suites fails, a file.failed.png and file.diff.png are also generated, showing the divergent screenshot and a contrast diff respectively, so you can verify that the changed behavior either does or does not reflect your patch. If you're confident that the screenshots reflect your change, you can update the new hashes manually in the test/results/results.json file, or update all hashes with the --write flag:

yarn test --write


The Python test suite is built on Pytest, and it asserts the correct behavior of the Python library.

Verbosity in the tests can be enabled with the --verbose flag.

Troubleshooting installation from source

If you are installing from a source distribution (sdist), make sure you have the System Dependencies installed.

Try installing in verbose mode:

pip install -vv perspective-python

The most common culprits are:

  • CMake version is too old
  • Boost headers are missing or too old

Timezones in Python Tests

Python tests are configured to use the UTC time zone. If running tests locally, you might find that datetime-related tests fail to assert the correct values. To correct this, run tests with the TZ=UTC, i.e.

TZ=UTC yarn test --verbose


You can generate benchmarks specific to your machine's OS and CPU architecture with Perspective's benchmark suite, which will generate a report.html file in the build/ directory of every package which supports benchmarks, as well as a results.json file in the bench/results/, which can be checked in to GIT with your changes to preserve them for future comparison.

yarn bench

The benchmarks report and results.json show a histogram of current performance, as well as that of the previous results.json. Running this should probably be standard practice after making a large change which may affect performance, but please create a baseline results.json entry for your test machine on a commit before your changes first, such that the effects of your PR can be properly compared.