在 TypeScript 的类型系统中，Top Type（顶层类型） 和 Bottom Type（底层类型） 是两个非常重要的概念。它们分别代表了类型范围的“最顶层”和“最底层”，理解它们对于掌握 TypeScript 的类型系统至关重要。

Time Picker Pnl in React Native

Why i write this component?
First, I found a lib called @react-native community/picker and wrote my code based on it. When I was done, it worked fine in ios, but when I turned on my android. Oh, my God, it’s not working. This component is platform based. It behaves differently on different platforms.

Then I found another library called react-native-picker, but it was too ugly and not customizable. My UI designer wouldn’t let me use this kind of thing, so I wrote my own component.

Note: This component is not perfect, but it works fine in my work. If you have any suggestion or issue, please let me know. You can build your own component based on this code.
If this code help you, please follow me on Github. XD(am greedy)

Requirements:

• react-native-modal: pop up modal for time picker

Classes

1
2
3
4
5
6
7
8
9
10
11

class Greeter {
  greeting: string

  constructor(message: string) {
    this.greeting = message
  }

  greet(): string {
    return "Hello, " + this.greeting
  }
}

Private

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

class Animal {
  constructor(private name: string) {}
}

class Horse extends Animal {
  constructor() {
    super("Horse")
  }
}

class Human {
  constructor(private name: string) {}
}

let animal = new Animal("Lucy")
let horse = new Horse()
let human = new Human("Jack")
animal = horse // success
animal = human // failed

川普不对伊朗动武 美股涨 金价回落 油价跳水

伊朗袭击美军驻伊拉克基地后，美国总统川普表示将升级经济制裁取代付诸武力。市场乐观情绪上扬，美股上涨，金价回落，油价则大跳水。

川普 1 月 8 日在白宫发表谈话，伊朗袭击并未伤害到任何美国人，称伊朗有所退让，暗示不会对伊朗动武，伊朗外交部长也称该国不寻求升级事态，这些消息都缓解了投资人对美伊局势的不安。

8 日美国股市上涨，道琼工业指数收涨 161.41 点或 0.56%，报 28745.09 点。标普 500 指数收涨 15.87 点或 0.49%，报 3253.05 点。那斯达克指数收涨 60.66 点或 0.67%，报 9129.24 点。费城半导体指数上涨 0.31 点或 0.02%，报 1867.59 点。

那斯达克指数创收盘新高，道琼工业指数、标普 500 指数、费城半导体指数徘回历史次高位。

Numeric enums

1
2
3
4
5
6
7
8
9
10
11
12

enum Direction {
  UP,
  DOWN,
  LEFT,
  RIGHT,
}

function move(length: number, direction: Direction): void {
  console.log(`move: ${direction} ${length}meters.`)
}

move(10, Direction.UP)

String enums

1
2
3
4
5
6

enum Direction {
  UP = "UP",
  DOWN = "DOWN",
  LEFT = "LEFT",
  RIGHT = "RIGHT",
}