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Frontend Monorepo Infrastructure

Since our frontend codebase for Penn Courses products are closely related, we've decided to opt for a monorepo version control system to allow for easier code-sharing and aid future development. Currently, the frontend/ directory houses 3 projects, namely Penn Course Alert, Penn Course Plan and pcx-shared-components, a library containing reusable React components/hooks that are used in both PCA and PCP.

Setting Up Development Environment

Make sure you have node (with a version that is ^18) and yarn installed. We use Yarn Workspaces to handle development dependency installation/resolution. In frontend/package.json, we have defined the directories of each project as a workspace, and running yarn install in frontend/ will install dependencies for each project to frontend/node_modules. Note that currently, both PCA and PCP have pcx-shared-components as a dependency as defined in their respective package.json configurations, so yarn will automatically symlink frontend/node_modules/pcx-shared-components to frontend/pcx-shared-components and both PCA and PCP codebases can use shared components simply by doing import _ from "pcx-shared-components".

Running the frontends

To run a frontend development server,

  1. cd frontend
  2. yarn to ensure dependencies are up-to-date.
  3. cd [alert|plan|review] depending on which frontend you'd like to run.
  4. yarn once more (just to be sure :))
  5. yarn dev to run the frontend.

Feel free to leave out the yarns when you know dependencies are up-to-date.

As long as the back-end is running on port 8000, requests will be proxied between the two development servers.

Modifications to CRA

By using Yarn Workspaces as described above, dependencies from another project are treated as an outside dependency, and therefore should be built and transpiled in order to make use of them. However, having to rebuild shared dependencies while working on another project introduces another layer to the build process during development, and cannot make use of hot-reloading directly. Therefore, we opted to modify CRA default Babel configurations to include all projects defined in the Yarn Workspace during transpilation, making it possible for hot-reloading set up in CRA to work as usual, even for editing code from another project that is set up as a dependency.

There are however some caveats. This makes use of react-app-rewired and customize-cra, which come with warnings that using these packages will "break the guarantees that CRA provides" and "no support will be provided". This will no longer be a concern when we move to next.js, since they support custom Webpack configurations out of the box. We also use get-yarn-workspaces in our Babel configurations to automatically include all projects defined in our Yarn Workspace as transpilation sources.

Pre-commit Hooks

To ensure our code base is consistent and adheres to good style, we also set up a pre-commit hook using husky to run Prettier and ESLint on all staged Javascript files. This makes use of lint-staged. Note that a commit will not succeed if it does not pass ESLint. It is important to note that eslint-disable next-line might not work as intended sometimes, since Prettier might reformat code such that the offending line is no longer directly below the ESLint hint. One can avoid this issue by using eslint-disable and eslint-enable for a block of code instead.

Pre-commit hooks are executed by lerna, which runs the script precommit in each workspace defined in their respective package.json configurations. These scripts all use lint-staged, which are configured in .lintstagedrc.yml.