typeScript学习

null 和 undefined

undefined any unknown 可以接受 undefined

let data: undefined = undefined
let data2: any = undefined
let data3: unknown = undefined

null any unknown 可以接受 null

let data4: null = null
let data5: any = null
let data6: unknown = null

let str: string | undefined = undefined
str = "abc"
console.log("str:", str)

// 可选参数?
function fn(data?: string) {
    if (data) data.toString()
}

function fn2(data: string | undefined) {

}
// 默认参数
function fn3(data: string = "abc") {

}
fn() // 参数可传可不传
// fn2() // 报错，参数必传
fn2(undefined)
fn3()