typescript.md

TypeScript

TypeScript adds static type checking to JavaScript, allowing for early error detection and more robust code. It also provides features like interfaces and generics, enhancing code quality and maintainability.

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• Configuration:
  • tsconfig.json - Main configuraiton file that controls TypeScript
• package.json scripts:
  • npm run compile - Compiles the TypeScript source in src/**/*.ts to plain JavaScript in dest/**/*.js
• package.json --save-dev Development Dependencies:
  • typescript - TypeScript is a strongly typed programming language that builds on JavaScript
  • ts-node - TypeScript execution and REPL for Node.js; used for both Jest tests and Swagger docs
  • @typescript-eslint/eslint-plugin - The tooling that enables ESLint and Prettier to support TypeScript
  • @typescript-eslint/parser - ESLint parser which leverages TypeScript ESTree to allow for ESLint to lint TypeScript source code
  • ts-jest - Jest transformer with source map support that lets you use Jest to test projects written in TypeScript

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.js/Extensionless ECMAScript Module Imports:

When importing modules use .js extension; ex: import foo from './path/to/lib.js'. The exceptions for this are things that are not compiled such-as the *.test.ts Jest tests and the ts-node driven swagger/serve_swagger_docs.ts Express HTTP API Swagger docs server.

NOTE: Jest tests will strip the .js extension off with the moduleNameMapper in jest.config.js meaning this convention works there as well.

Examples:

//
//  Application `*.ts` module
//

// ✅ Works! Language server processing works as well!
import { GreetingHelper } from './lib/GreetingHelper.js';

// ❌ WILL NOT WORK!
// - Module will not be found on run
// - Causes issues with nested imports when ran from Jest
// - OK to use in ts-node ran Jest tests and Swagger docs!
import { GreetingHelper } from './lib/GreetingHelper';