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Object 范围太广
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object ：Object除去基本类型之外的类型
索引签名Record-
Class or Constructor
type A = {
[k:string] : number
}
type Record<K extends number | string | symbol, T> = {
[k in K] : T
}
const person: Record<string,number> = {
name: 'frank',
age: 12
}
type Person = {
username: string
age: number
sayHi: FnWithThis
}
type FnWithThis = (this:Person,name) => void
const sayHi:FnWithThis = function(){
console.log(this.username)
}
const person:Person = {
username: 'frank',
age: 12,
sayHi: sayHi
}
// 调用必须指定this
person.sayHi() // 'frank'
or
sayHi.call(person) // 'frank'
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never：侧重于类型推导，推到不可能出现的情况，就是never
type A = string | number | boolean
let a:A
if(typeof a === 'string'){
a.indexOf
}else if(typeof a === "number"){
a.toFixed
}else if(typeof a === "boolean"){
a.valueOf
}else{
a // type is never
}
