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Object Playground

Object Playground is a tool for visualizing and experimenting with JavaScript object relationships. It's online at Object Playground is a project from Let's Code: Test-Driven JavaScript, a screencast series focused on professional, rigorous JavaScript development. Created by James Shore.

This repository contains the source code for Object Playground.

Browser Support

Object Playground has been tested against the browsers listed at the top of Jakefile.js. At the time of this writing, the following browsers are known to work. Other modern browsers are likely to work as well.

  • Chrome 40
  • Firefox 36
  • IE 10
  • IE 11
  • Safari 8.0 (Mac)
  • Safari 7.0 (iOS)

The following browsers are known to not work:

  • IE 9: Lacks the Int32Array type used by Viz.js. A polyfill was attempted, but resulted in an "out of memory" error.
  • IE 8: Does not support SVG, lacks Int32Array type.

Building and Testing

Before building for the first time:

  1. Install Node.js. Use the version described in Jakefile.js NODE_VERSION variable. (The npm n package can help with changing Node versions.)
  2. Download the source code by cloning the git repository: git clone
  3. All commands must run from the root of the source tree: cd <directory>.
  4. To cause the build to fail unless certain browsers are tested, edit TESTED_BROWSERS at the top of Jakefile.js.

To build (and test):

  1. Run ./ karma (Unix/Mac) or jake karma (Windows) to start the Karma server.
  2. Point the browsers you want to test against at the URL http://localhost:8080.
  3. Run ./ (Unix/Mac) or jake (Windows) every time you want to build and test. Use the loose=true option to relax the Node.js and browser version requirements.

Note: At the time of this writing, the source code has not been confirmed to build on Windows.

To test manually:

  1. Run ./ run.
  2. Open http://localhost:8080 in a browser.

(Or just open src/index.html in a browser.)

Development and Integration

This repository contains two branches:

  • master is for development.
  • integration is guaranteed to build and pass all tests.

To integrate:

  1. Get to a clean build and commit your code to the master branch.
  2. Run ./ (Unix/Mac) or integrate (Windows) to test the master branch and merge it into the integration branch.

To change code samples:

  1. Use to convert code to JavaScript string.
  2. Modify src/user_code.js with new sample.


Before deploying for the first time:

  1. Install rsync or make sure it's available on the path
  2. Modify PRODUCTION_HOST at top of deploy.jakefile to match production host (using username@host format)
  3. Modify PRODUCTION_DIR at top of deploy.jakefile to be the directory on the host where your public web content goes

To deploy:

  1. Run ./ latest (Unix/Mac) or deploy latest (Windows) to integrate the master branch and deploy it. The script will tag your git repository with deploy-<date>-<timestamp> if the deploy succeeds.

In case of a bad deployment:

  1. Choose a previous, good commit to deploy. gitk --all and the deploy tags may be helpful here.
  2. Check out the commit: git checkout <commit_id>
  3. Run ./ head (Unix/Mac) or deploy head (Windows) to deploy the commit. As above, the script will tag the git repository if the deploy succeeds.


A tool for visualizing and experimenting with JavaScript object relationships.







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