Introduce ESLint, typescript-eslint and Prettier

[0918nobita]

Fixes: #14

Summary

• Install packages
  • eslint (Linter for ECMAScript)
  • @typescript-eslint/parser (Alternative ESLint parser for TypeScript)
  • @typescript-eslint/eslint-plugin (ESLint plugin for adding TypeScript-related rules)
  • prettier (Code formatter for various languages, including JavaScript)
  • eslint-config-prettier (Turns off all rules that are unnecessary or might conflict with Prettier)
  • eslint-plugin-prettier (Runs Prettier as an ESLint rule and reports differences as individual ESLint issues)
• Add configuraton files
  • /.eslintrc.js
  • /.prettierrc.js
• Add npm scripts
  • lint (Runs ESLint without changing code)
  • format (Runs ESLint and fixes issues automatically with overwriting code)
• Run the format script, then fix code manually for reducing ESLint issues

Screenshots

Result of executing npm run lint command:

VS Code + ESLint extension:

[antfu]

Do we really need ESLint+Prettier? Seems a bit too heavy to me. 😅

[0918nobita]

Indeed, it might be better to introduce only Prettier now. I'll close this PR and create PR again to try out only Prettier.