TypeScript 是一种静态类型的编程语言,它可以帮助开发者在编写代码时捕获一些潜在的错误。在 TypeScript 中,isPossiblyUndefined 是一个类型保护,用于判断一个变量是否可能是未定义的。这种类型保护对于防止在运行时遇到未定义变量引发的问题非常有用。 当使用 isPossiblyUndefined 时 在我们的代码中使用 isPossiblyUndefin...
解决方案:加类型断言 (this.toolsasArray<any>).forEach(item=>{console.log(item.id);})
解决办法就是加一个判断 因为这里find()能够拿到正确的数据,所以else语句不会执行,只要返回非undefined且符合我们定义的泛型类型的数据最后得到的结果就不会包含undefined了
Is this a regression? Yes Description type User = { role: "guest-user" | "user" | "none" }; public user = signal<User | undefined>(undefined); public user$ = toObservable(this.user).pipe(filter((user) => user !== undefined)); ...
我得到Object is possibly 'undefined'一个prop string是从父母传下来的component。所述string被内限定INITIAL_STATE在`作为父 private static INITIAL_STATE = { password: '' }; 这意味着子组件中的propforpassword永远不应该是undefined. 子组件是 interface InterfaceProps { onlyOneLeft?: boolean; isEnabled?:...
functionbroken(name: string |null): string {functionpostfix(epithet: string) {returnname.charAt(0) + '. the ' + epithet;//error, 'name' is possibly null} name= name || "Bob";returnpostfix("great"); }functionfixed(name: string |null): string {functionpostfix(epithet: string) {return...
declare let strs: string[] | undefined; // Error! 'strs' is possibly undefined. let upperCased = strs.map(s => s.toUpperCase()); // 'strs!' means we're sure it can't be 'undefined', so we can call 'map' on it. let lowerCased = strs!.map(s => s.toLowerCase());...
== undefined) { feeObj[property] + 2; // still error, possibly undefined! } } It's because the type of property is string, which is not a literal type, and currently the narrowing behavior operates only on the types of the property keys, not their identities. From the type sy...
Typescript is saying that change or data is possibly undefined (depending on what onUpdate returns). So you should wrap it in a null/undefined check: if(change && change.after && change.after.data){ const data = change.after.data(); const maxLen = 100; const msgLen = data.m...
required in type 'C'. console.log(c.foo.toString()) // Error, Object is possibly 'undefined...