建议补充一节列举ts 不那么好用的地方

[qiulang]

从我自己使用经验，我真的体会到ts有时候不那么好用，引入的问题比起要解决问题反而更麻烦，举几个例子

1. nodejs 18 引入的fetch 没法很好的用ts标注，这个问题单 node@18.x.x version not fetch global api ? DefinitelyTyped/DefinitelyTyped#60924 说得很清楚： 还没人能完全搞清楚怎么标注fetch好， 所以目前变通方法都让人感觉很麻烦

The short version is that no one has implemented the types for fetch in this package yet. There are some ideas about how best to handle it but I don't know if there is actually a consensus among maintainers of this package. If you'd like to help with that, DT has good guidelines for getting started as a contributor, and I'm sure several people on this thread would be eager to review a MR.

2. narrow 这个功能没法对object的key生效，参见这个问题单 Narrowing for key type by in operator microsoft/TypeScript#43284
   所以在js 本来很简单，遍历 Object key的代码在ts 反而变得很麻烦

let options = {
    foo: 'bar',
    bar: 'baz',
}

for (const [key, value] of process.argv) {
    if (key in options) {
        options[key] = value; // 报错，尽管我已经在if 里
    }
}

进一步数组的 reduce 方法标注就会变得很复杂，参见 https://stackoverflow.com/questions/52856496/typescript-object-keys-return-string

[ruanyf]

多收集一些材料，可以加这一章，作为使用 TypeScript 的注意点。

目前，只把遇到的问题，插在相应章节里面。