Typescript promise type in then

Question

为什么在块会话是空的，如何修复它?

打印稿沙箱。

type X = {id: string, session: {smt: string} | null}
const x1 = new Promise<X>(resolve => {
resolve('smth' as unknown as X)
})
x1.then((user)=>{
if (!user.session) throw new Error('e')
user.session.smt // ok
return user
})
.then(user=>{
user.session.smt // why session is nullable again?
})
.catch(e=> e)

Answer 1

TypeScript不知道user对象在此期间没有被修改。例如，其他人可能做了:

x1.then((user)=>{
user.session = null; // that's allowed
})