类型收窄之前只能使用公共方法
JS方法
typeof
缺点
- typeof null —→ object
- typeof 数组 —→ object
- typeof 日期 —→ object
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：
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type Person {
name: string
}
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- key in obj
- Array.isArray()
????????类型谓词is
重点在 shape is Rect
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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
}
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????????????????可辨别联合
要求：T = A | B | C
- A | B | C … 要有一个相同的属性 type或其它
- type类型只能为 简单类型
- A | B | C …的type属性无交集
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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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