断言函数 Posted on Jan 13, 2021 https://jkchao.github.io/typescript-book-chinese/new/typescript-3.7.html#%E6%96%AD%E8%A8%80%E5%87%BD%E6%95%B0 https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions