Live Note

Remain optimistic

Posted on Edited on In

Interface

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interface labelValue {
  label: string
}

function printLabel(obj: labelValue): void {
  console.log(obj.label)
}

let obj = { size: 10, label: "some text" }
printLabel(obj)

Optional Properties

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interface SquareConfig {
  color?: string
  width?: number
}

function createSquare(config: SquareConfig): { color: string; area: number } {
  let defaultSquare = { color: "White", area: 200 }
  if (config.color) defaultSquare.color = config.color
  if (config.width) defaultSquare.area = config.width ** 2

  return defaultSquare
}

console.log(createSquare({ color: "Black", width: 30 }))

Readonly Properties

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interface Point {
  readonly x: number
  readonly y: number
}

let readOnlyArray: ReadonlyArray<number> = [1, 2, 3, 4]
let a: number[] = readOnlyArray as number[] // readonly array assignment to ordinary array

Excess Property Checks

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interface SquareConfig {
  color?: string
  width?: number
  [propName: string]: any
}

let newSquare = createSquare({ width: 100, opacity: 0.5 } as SquareConfig)
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Introduction

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interface A {
  text: string
}

class B {
  text: string
}

let a: A = new B() // no error

At least same member

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interface A {
  text: string
}

function foo(obj: { text: string }): string {
  return obj.text
}

let obj = { text: "some text", num: 3 }
let a: A = obj // success
foo(obj) // success
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Posted on Edited on In

基本类型

  • boolean:
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    let done: boolean = true
  • number:
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    let count: number = 20
  • string:
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    let name = "Edward Wang"
  • array:
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    let list1: number[] = [1, 2, 3]
    let list2: Array<number> = [1, 2, 3]
  • tuple:
    1
    let x: [string, number] = ["test", 2]
  • enum:
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    enum NUMBER {
      ONE,
      TWO,
      THREE,
    }
    let a = NUMBER.TWO
    let title: string = NUMBER[3]
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Generics

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function foo<T>(arg: T): T {
  return arg
}

function len<T>(arg: Array<T>): Array<T> {
  console.log(arg.length)
  return arg
}

Generics Types

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function foo<T>(arg: T): T {
  return arg
}

interface fooInterface<T> {
  (arg: T): T
}

let myFunction: <T>(arg: T) => T = foo
let otherFunction: { <T>(arg: T): T } = foo
let interfaceFunction: fooInterface<number> = foo
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Posted on Edited on In 
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const enum Foo {
  AA = "aa",
  BB = "bb",
}

type B = keyof typeof Foo // 'AA' | 'BB'

// Template Literal Types
type C = `${keyof { [x in Foo]: string }}`
// 'aa' | 'bb'