functiontoUpperCase(x:unknown){if(isString(x)){x.toUpperCase();// ⚡️ x is still of type unknown}} TypeScript throws an error. We can be sure that x is of type string at this point. But since the validation is wrapped in a function, the type of x does not change (as opposed...
constmyVar:string|number='hello world';console.log(typeofmyVar);// 👉️ "string"if(typeofmyVar ==='string') {console.log(myVar.toUpperCase());// 👉️ "HELLO WORLD"}// ✅ Use instanceof for classesclassPerson{}constperson =newPerson();console.log(personinstanceofPerson);// 👉...
functionprintValue(value:string|number):void{if(typeofvalue ==='string') {console.log(`The value is a string:${value}`);}elseif(typeofvalue ==='number') {console.log(`The value is a number:${value}`);}}classPerson {name:string;...
For example, this change to a function in a .d.ts file adding a new param to a function: index.d.ts: - export function twoslash(body: string): string + export function twoslash(body: string, config?: { version: string }): string <my-package>-tests.ts: import {twoslash} from "...
interface A { a: string; } interface B { b: string; } type MyType = A | B; function isA(x: MyType): x is A { return "a" in x; } function someFn(x: MyType) { if (isA(x) === true) { console.log(x.a); // works! } } We’d like to thank Mateusz Burzyński fo...
Property 'name' does not exist on type '{ firstName: string; lastName: string; role: string; }'.TypeScript 5.8 is now available What is TypeScript? JavaScript and More TypeScript adds additional syntax to JavaScript to support a tighter integration with your editor. Catch errors early in ...
const message: string = greet('John'); console.log(message); // Output: "Hello, John!" 延伸阅读:TypeScript 官方网站(https://www.typescriptlang.org/) 2.解释 TypeScript 中静态类型的概念及其好处。 答案:TypeScript 中的静态类型可以在开发过程中指定变量、函数参数和返回值的数据类型。这有助于及...
string().base64(); Check out validator.js for a bunch of other useful string validation functions that can be used in conjunction with Refinements. You can customize some common error messages when creating a string schema. const name = z.string({ required_error: "Name is required", ...
letname:string="甜甜"; Number类型 代码语言:javascript 复制 constcount:number=10; 布尔类型(boolean) 代码语言:javascript 复制 constflag:boolean=true; undefined和null 注意:如果开启了严格模式,需要在tsconfig.json文件中修改为"strictNullChecks":false,这样,undefined和null可以赋值给其他类型,否则null和undefined...
functioncheckPermission(permission:string){returnfunction(target:any){constoriginalConstructor=target;constnewConstructor=function(...args:any[]){// 检查用户权限的逻辑if(!hasPermission(permission)){thrownewError(`没有权限进行操作:${permission}`);}returnneworiginalConstructor(...args);};newConstructor.pr...