typescript - 在 Typescript 中使数组元素可为空

Question

我很惊讶这段代码没有错误:

let myList: string[] = require('something')

let foo: string | undefined = myList[7]

foo.length // no error!

如何让 foo 具有类型 string |未定义?

我希望 typescript 编译器在第三行引发 Object is possible 'undefined'.ts(2532)。

Answer 1

您可以将数组访问的结果“转换”为(string|undefined)

let myList : string[] = require('something');
let v = myList[7] as (string | undefined); //v will have type string|undefined
let uv = v.length;  //will give an error that v is possibly undefined