Added ESLint + Prettier and GitHub Actions lint workflow

[Mehulantony]

This PR introduces automated code quality enforcement to the OSS Rerum Playground project to improve code maintainability, consistency and contributor experience across the codebase.

What was added:

1. ESLint integrated with recommended rules and Prettier; created eslint.config.js file.
2. .prettierrc.json and .prettierignore for consistent formatting
3. .gitignore updated to exclude node_modules
4. GitHub Actions workflow (lint.yml) to automatically run:

• npm run lint (ESLint)
• npm run format (Prettier check)

Why this is important?

1. Previously, the project did not have automated code quality checks, which could allow inconsistent formatting, undefined variables, or accidental errors into main.

2. With a lint workflow running on every push and pull request, contributors get immediate feedback and poorly formatted/unsafe code is prevented from merging. It also makes the codebase easier to debug, maintain and extend.

Impact on existing codebase:

1. Running npm run lint:fix resulted in formatting cleanup across several JS files.
2. No functional changes were made — all modifications are style-only (whitespace, indentation, missing semicolons, etc.)
   3.The application behavior remains unchanged.

How to run locally:

1. npm install
2. npm run lint – check for problems
3. npm run lint:fix – auto-fix formatting

*CI automatically runs these checks on PRs and pushes

[Copilot]

Pull Request Overview

This PR introduces automated code quality enforcement by adding ESLint, Prettier, and a GitHub Actions lint workflow to the OSS Rerum Playground project. The changes standardize code formatting across JavaScript files and establish automated checks for future contributions.

Key Changes:

• Added ESLint v9.39.1 with Prettier integration for code linting and formatting
• Created GitHub Actions workflow to run lint and format checks on pushes and PRs
• Applied automated formatting fixes to multiple JavaScript files (style-only changes)

Reviewed Changes

Copilot reviewed 13 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
package.json	Added ESLint, Prettier, and related plugins as dev dependencies with npm scripts for linting and formatting
package-lock.json	Lockfile for npm dependencies
eslint.config.js	ESLint flat config with Prettier integration and browser globals
.prettierrc.json	Prettier formatting rules (100 char width, 2 space tabs, single quotes)
.prettierignore	Excludes node_modules, dist, vendor, and minified files from formatting
.gitignore	Added node_modules/ to version control exclusions
.github/workflows/lint.yml	CI workflow to run ESLint and Prettier checks on PRs and main branch pushes
web/js/utilities.js	Applied automated formatting (indentation, spacing, semicolons, quote style)
web/js/toolsCatalog.js	Applied automated formatting
web/js/tools.js	Applied automated formatting; contains duplicate code that needs removal
web/js/sandbox.js	Applied automated formatting
web/js/playground.js	Applied automated formatting
web/js/manifestStorage.js	Applied automated formatting
web/js/json-utils.test.js	Applied automated formatting
web/js/json-utils.js	Applied automated formatting
web/js/config.js	Applied automated formatting

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[Copilot]

The window.updateToolOrder function is defined twice in this file (lines 194-200 and lines 300-306). This creates duplicate code that should be removed. Keep only one definition of this function.

[Copilot]

The DOMContentLoaded event listener is registered twice (lines 202-214 and lines 308-320). This will cause the initialization code to run twice, which is unnecessary and could lead to unexpected behavior. Remove one of these duplicate listeners.

[Copilot]

The ignores property is placed inside the configuration object, but in ESLint's flat config format, ignores should be a top-level property in a separate configuration object. This should be:

module.exports = [
  {
    ignores: ["node_modules/", "web/dist/", "web/vendor/", "web/**/*.min.js", "web/**/*.test.js"]
  },
  {
    files: ["web/**/*.js"],
    // ... rest of config
  }
];

[Mehulantony]

This is a good suggestion. ESLint supports "ignores" inside the same config object in Flat Config as well as in a separate top-level block. Since the current placement of code works and keeps the PR minimal, I will not be making this change now. We can revisit this later if needed for clarity.

[Mehulantony]

The CI workflow was failing earlier (Prettier checks failing) because HTML, CSS and JSON files had formatting differences. Auto-formatting these files would involve huge changes and could potentially introduce visual/UI regressions.

In order to avoid this, a modification was made to "package.json" file to only check JavaScript files which aligns with the linting rules already implemented in this project and ensures consistent style enforcement without touching other unrelated assets. These adjustments allowed the GitHub Actions CI pipeline to complete with a green check, confirming that the linting and formatting checks pass reliably for all JS files moving forward.

Some ESLint warnings (mainly related to unused variables in legacy functions) still appear during the linting process, and is visible in the GitHub Actions workflow. These warnings do not impact the functionality of the application, and addressing them would require modifying production JavaScript logic, which is outside the scope of this CI/CD-focused PR. To avoid unintentionally changing behavior in a user-facing codebase, these warnings were left untouched.

The CI workflow is configured to report these warnings without failing, allowing maintainers to be aware of them while ensuring the pipeline remains stable.

[Mehulantony]

Included changes to Rerum's .gitignore file to exclude common temporary, system, dependency and IDE-specific files which should not be tracked in version control. This update helps ensure that the project repository is clean and prevents accidentally committing large files, thereby improving developer experience. No production code is affected by this change.