TS 类型收窄教程示例详解

目录JS方法

目录

类型收窄之前只能使用公共方法

JS方法

typeof

缺点

a instanceof A : A 是否出现在a的原型链上

缺点

不支持string 、number 、boolean 等原始类型

不支持TS的 自定义类型，如下：

type Person {
  name: string
}

类型谓词is

重点在 shape is Rect

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 * sphphape.radius ^ 2
  }
}
const isRect = (shape: Rect | Circle): shape is Rect => {
  return 'width' in shape && 'height' in shape
}

可辨别联合

要求：T = A | B | C

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
  }
}

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