TS类型收窄教程示例详解

type Person {
  name: string
}

type Rect = {
  width: number
  height: number
}
type Circle = {
  center: [number, number]
  radius: number
}
const area = (shape: Rect | Circle): number => {
  if(isRect(shape)) {
    return shape.width * shape.height
  } else {
    return Math.PI * shape.radius ^ 2
  }
}
const isRect = (shape: Rect | Circle): shape is Rect => {
  return 'width' in shape && 'height' in shape
}

type Rect = {
  type: 'rect',
  width: number
  height: number
}
type Circle = {
  type: 'circle'
  center: [number, number]
  radius: number
}
const area = (shape: Rect | Circle): number => {
  if(shape.type === 'rect') {
    return shape.width * shape.height
  } else {
    return Math.PI * shape.radius ^ 2
  }
}