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
主要代码: interface Example { children?: Example[] } const example: Example = { children: [{ children: [] }] } if (example.children) { for (let i = 0; i < example.children.length; i++) { if (example.children[i] && example.children[i].children) { console.log(example.children[...
The code in publicuser$=toObservable(this.user).pipe(filter((user)=>user!==undefined)); doesnotresult inusers$being of typeUser, as thefilteroperator is not a type-guard. Only from TypeScript 5.5 onwards would theuser !== undefinedreturn expression result in inferring a type-guard ofuser...
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...
I think the problem is that arrow functions don't have a 'this' try using an old school function definition? this remains an issue TS2532: Object is possibly 'undefined'. @pre<RoleEntity>('save', (next) => { if (!this.createdAt) { this.createdAt = this.updatedAt = new Date() }...
In this code, ifgetUser()returns null or undefined, theuservariable will be assigned the default object{ name: 'John Doe'}. Examples Let’s look at some examples to further illustrate how to handle the “Object is possibly null” error: ...
因為通常您可能比類型系統還了解情況,所以我們也引進了一個後置的!運算子,讓null和undefined從類型中排除掉。 复制 declare let strs: string[] | undefined; // Error! 'strs' is possibly undefined. let upperCased = strs.map(s => s.toUpperCase()); ...
address.toString()); // Error: [ts] Object is possibly 'undefined'. if (person.address != undefined) { console.log(person.address.toString()); //Ok. as we checked the type } Index Type Query - keyof keyof 定义了一个Type, 这个Type的值来自于指定的类。 代码语言:javascript 代码运行次数...