javascript - vue原始碼中?:之間無間隔使用是什麼意思？

Question

isReservedTag: (x?: 字串) => boolean;
isReservedAttr: (x?: string) =>布林值;
parsePlatformTagName: (x: string) =>字串;
isUnknownElement: (x?: string) => boolean;
getTagNamespace: (x?: string) =>;字串| void;
MustUseProp: (標籤: 字串, 類型: ?字串, 名稱: 字串) =>布林值；

Answer 1

flow 的類型系統

Answer 2

見這個回答/q/10...