投稿者: admin_wp

% npx tsc --init

Created a new tsconfig.json with:                                               
                                                                             TS 
  target: es2016
  module: commonjs
  strict: true
  esModuleInterop: true
  skipLibCheck: true
  forceConsistentCasingInFileNames: true


You can learn more at https://aka.ms/tsconfig

// union & intersection of types
type Cat = {name: string, purrs: boolean}
type Dog = {name:string, barks: boolean}
type CatOrDog = Cat | Dog
type CatAndDog = Cat & Dog

let a_o: CatOrDog = {
    name: 'ball',   // need not to specify all properties
    barks: false
}

let a_a: CatAndDog = {
    name: "Dounald",
    barks: false,   // need to specify all properties of the Dog and Cat
    purrs: false
}

// object, Object and {}
let o1: {}
let o2: object
let o3: Object  // Object is an interface

o1 = {a: 2} // object
o1 = 123    // primitive

o2 = {a: 2}
//o2 = 123  // primitive is not usable

o3 = {a: 2}
o3 = 123

o1 = {toString() {return 1}}    // accept any type of object
//o3 = {toString() {return 1}}    // treat o3 as a string type which is a predefined type

// unknown type 
let aa: unknown = 10    // type safe 'any'
let cc = aa === 10      // === is usable
console.log(cc)

//let dd = aa + 20      // -> cause error
if (typeof aa === 'number'){
    let dd = aa + 20
    console.log(dd)
}


// any type
let aaa: any = 10    // type safe 'any'
let ccc = aa === 10
console.log(ccc)

let ddd = aaa + 20
ddd = aaa + 20
console.log(ddd)

% ts-node "./hello.ts"
true
30
true
30

// type of unknown
let hh: unknown = 10
if (typeof hh === "number"){
    let hh_m = hh * 3
    console.log(hh_m)
}