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A web-based IDE for JavaScript, without the "bad parts". See for more information.

This is a README to get started hacking on Ocelot.

Dependencies and Cloud Configuration

  1. Install Node and the Google Cloud SDK on your development machine. We use Node 14.

  2. Create a project on Google Cloud Platform to host Ocelot. You can reuse an existing project, as long as you don't mind setting Cloud Datastore to Datastore mode permanently for that project. If you are already using Cloud Datastore in Native mode, you will need to create a new project.

  3. A domain to host Ocelot. For example, you can use a subdomain of, if you do not want to pay for a domain name,

  4. Ensure your development machine is logged in to the Google Cloud Platform

    gcloud auth login
    gcloud auth application-default login
  5. Create a project on Google Cloud Platform and note down its Project ID. If this is the only Google Cloud project that you are using, you can set it as the default project on your machine:

    gcloud config set project PROJECT_ID

    Otherwise, you will have to add the --project PROJECT_ID flag to all subsequent commands that manipulate Google Cloud resources. The remaining instructions assume that you set the default project.

  6. Create a bucket for Ocelot to store files. For example, the following command creates a bucket called ocelot-ide-org-files, and sets the storage class to regional, which is a cheaper storage option than the default, which replicates data across multiple data centers. The -b on flag disables per-file ACLs and isn't strictly necessary.

    gsutil mb -b on -c Regional -l us-central1 gs://ocelot-ide-org-files
  7. Create a bucket for Ocelot to store revision history. For example:

    gsutil mb -b on -c Regional -l us-central1 gs://ocelot-ide-org-history
  8. Enable object versioning on the former bucket. Ocelot relies on object versioning to implement its history feature:

    gsutil versioning set on gs://ocelot-ide-org-history
  9. Using your web browser, go to the Google Cloud Datastore console and create a database in Datastore Mode. (Do not use Native Mode.) You will need to chose the datastore location. We recommend choosing the same region that you used for the two buckets that you created above.

  10. Using your web browser, configure the OAuth consent screen for the Google Cloud project. It is straightforward to setup the application for testing, which limits you to 100 users over the lifetime of the testing period.

  11. Using your web browser, go to the Credentials page for the Google Cloud project. Click the Create Credentials button and then click OAuth client ID. On the next page, select Web application as the application type and enter the domain name at which you plan to host Ocelot.

  12. Using your web browser, Enable the Google Cloud Build API and the Stackdriver Error Reporting API

  13. Copy the file /env.yaml to /backend/env.yaml and edit it as directed in the file.

Building and Deploying the Ocelot backend

cd backend
npm install
npm run-script build
npm run-script deploy

Building and Deploying the Ocelot frontend

Edit the file frontend/src/secrets.ts.

Run the following commands:

cd frontend
npm install
npm run-script build

At this point, you need to deploy the contents of frontend/build to a static web hosting provider. For example, if you plan to use GitHub Pages, you can create a repository with the contents of frontend/build, push that repository to a new GitHub pages, and serve it.


Copyright 2018--2020 University of Massachusetts Amherst

Copyright 2019--2021 University of Texas at Austin

Copyright 2020--2021 Northeastern University

Old Instructions Below

To setup and run backend locally

cd Ocelot/backend
yarn install
yarn run build && yarn run serve

Development Instructions

Occasionally, you will want to hack on ElementaryJS (EJS), and will want to test out your changes before deploying them. To do so:

  1. Clone EJS:
  2. Install dependencies of EJS and build it (from within the EJS dir):
    yarn install
    yarn build
    yarn test
  3. Hack on EJS code, and re-build.
  4. Tell yarn to make the local version of EJS available to other projects (still within the EJS dir):
    yarn link
    Yarn should then tell you:
    yarn link v1.10.1
    success Registered "@stopify/elementary-js".
    info You can now run `yarn link "@stopify/elementary-js"` in the projects where you want to use this package and it will be used instead.
    Done in 0.03s.
  5. Change to the Ocelot frontend dir, delete any cached EJS libs, and tell yarn to use the local version of EJS:
    rm -rf node_modules/@stopify/elementary-js
    yarn link "@stopify/elementary-js"
    Yarn should tell you:
    yarn link v1.10.1
    success Using linked package for "@stopify/elementary-js".
    Done in 0.18s.
  6. Compile the ocelot frontend, and deploy it locally:
    yarn build && yarn serve-local
  7. Further changes to EJS will not require you to run the "link" steps again. Yarn remembers that you told it to use the local versions. Just recompile both EJS and the Ocelot frontend.

Once you are done hacking on the local EJS changes:

  1. Push a PR to EJS with the updates and the version number updated in package.json for EJS.
  2. Run npm publish to update the published version of EJS
  3. Create an Ocelot PR to use the newly deployed version of EJS by editing the EJS version number in package.json in Ocelot/frontend
  4. To tell yarn to go back to the published version of EJS: In the Ocelot/frontend directory:
yarn unlink "@stopify/elementary-js"
yarn install

Issues you may have

  • Delete this directory: rm -rf Ocelot/node_modules

  • There is a bug in the latest Yarn (1.7) that gives a stupid error when you use yarn install or yarn add after running yarn link:


    So, first run:

    yarn unlink stopify && yarn unlink elementary-js && yarn link stopify-continuations

    Then run yarn install or yarn add ...:

    then in Ocelot/frontend, run:

    yarn link stopify && yarn link elementary-js && yarn link stopify-continuations