TS-COMMON

Requirements

• TypeScript version: >=3.5.1
• ECMAScript target version: ES2019

Why do we need another set of JS libraries?

Because we would like to have

1. TypeScript native libraries instead of using '@types'
2. functional style libraries
   1. functions without side-effects
   2. immutable data
3. Target the the latest ES standard and use the latest TS & ES features such as asynchronous iterators.

Recommendations

• https://standardjs.com/rules.html
• Conventions over configuration
• No sequential coupling. See https://en.wikipedia.org/wiki/Sequential_coupling
• No object inheritance. Use
  • composition,
  • unions, or
  • discriminated unions
• No any type, use unknonw instead
• Use read only types.
  • readonly T[] instead of T[],
  • readonly [A, B] instead of [A, B],
  • readonly properties.
• No var. Use const instead. In some cases, use let.
• No export class. Use export interface and export function instead.
• No null. Use undefined instead.
• String index property type should be a superset of undefined.
  • Incorrect { [key: string]: T }
  • Correct { [key: string]: undefined|T }
• No lodash.. Use native lazy TypeScript libraries (such as ts-common/iterator) or lazy.js.
• No throw. Alternatives
  • return errors,
  • use callback function (dependency injection).
• No clone, cloneDeep. Use immutable data to avoid cloning.
• No Symbol("..."). Use Symbol.for("...") instead.
• No { function(); } declaration in the interface. Use { readonly property: () => void } instead.
• No as operator. Use type narrowing.
• No is operator. Use discriminators.

TypeScript Repository Initialization

1. npm init
2. npm install -D typescript @types/jest jest jest-junit tslint tslint-immutable
3. package.json:

   "scripts": {
       "tsc": "tsc",
       "test": "tsc && tslint -p tsconfig.json && jest",
       "prepack": "npm install && tsc"
   },
   "jest": {
     "testEnvironment": "node",
     "testMatch": [
       "**/dist/test/*test.js"
     ],
     "reporters": [
       "jest-junit",
       "default"
     ],
     "collectCoverage": true,
     "collectCoverageFrom": [ "dist/*.js"],
     "coverageThreshold": {
       "global": {
         "branches": 100,
         "functions": 100,
         "lines": 100,
         "statements": 100
       }
     },
     "coveragePathIgnorePatterns": [
       "/dist/test/"
     ],
     "coverageReporters": [
       "cobertura",
       "text",
       "html"
     ]
   },
   "jest-junit": {
     "outputDirectory": ".",
     "outputName": "test-results.xml"
   },
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
   "files": [
       "dist/index.d.ts",
       "dist/index.d.ts.map",
       "dist/index.js.map",
       "dist/index.js",
       "src/index.ts"
   ],

4. npm run tsc -- --init
5. tsconfig.json
6. Create src/index.ts
7. .gitignore:

   *.js
   *.d.ts
   *.map
   test-results.xml
   

8. azure-pipelines.yml
9. tslint.json

Optional

1. Save the Visual Studio Code workspace.